qmckl/org/qmckl_ao.org

#+TITLE: Atomic Orbitals
#+SETUPFILE: ../tools/theme.setup
#+INCLUDE: ../tools/lib.org

The atomic basis set is defined as a list of shells. Each shell $s$ is
centered on a nucleus $A$, possesses a given angular momentum $l$ and a
radial function $R_s$. The radial function is a linear combination of
\emph{primitive} functions that can be of type Slater ($p=1$)  or
Gaussian ($p=2$):

\[
  R_s(\mathbf{r}) = \mathcal{N}_s |\mathbf{r}-\mathbf{R}_A|^{n_s}
  \sum_{k=1}^{N_{\text{prim}}} a_{ks}\, f_{ks}
 \exp \left( - \gamma_{ks} | \mathbf{r}-\mathbf{R}_A | ^p \right).
\]

In the case of Gaussian functions, $n_s$ is always zero.
The normalization factor $\mathcal{N}_s$ ensures that all the functions
of the shell are normalized to unity. Usually, basis sets are given
a combination of normalized primitives, so the normalization
coefficients of the primitives, $f_{ks}$, need also to be provided.

Atomic orbitals (AOs) are defined as

\[
\chi_i (\mathbf{r}) = \mathcal{M}_i\, P_{\eta(i)}(\mathbf{r})\, R_{\theta(i)} (\mathbf{r})
\]

where $\theta(i)$ returns the shell on which the AO is expanded,
and $\eta(i)$ denotes which angular function is chosen.
Here, the parameter $\mathcal{M}_i$ is an extra parameter which allows
the normalization of the different functions of the same shell to be
different, as in GAMESS for example.

In this section we describe first how the basis set is stored in the
context, and then we present the kernels used to compute the values,
gradients and Laplacian of the atomic basis functions.

* Headers                                                          :noexport:
  #+begin_src elisp :noexport :results none
(org-babel-lob-ingest "../tools/lib.org")
  #+end_src


  #+begin_src c :tangle (eval h_private_type)
#ifndef QMCKL_AO_HPT
#define QMCKL_AO_HPT

#include <stdbool.h>
  #+end_src

  #+begin_src c :tangle (eval c_test) :noweb yes
#include "qmckl.h"
#include "assert.h"
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>
#include <math.h>
#include "chbrclf.h"

int main() {
    qmckl_context context;
    context = qmckl_context_create();
  #+end_src

  #+begin_src c :tangle (eval c)
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#ifdef HAVE_STDINT_H
#include <stdint.h>
#elif HAVE_INTTYPES_H
#include <inttypes.h>
#endif

#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <assert.h>

#include "qmckl.h"
#include "qmckl_context_private_type.h"
#include "qmckl_memory_private_type.h"
#include "qmckl_memory_private_func.h"
#include "qmckl_ao_private_type.h"
#include "qmckl_ao_private_func.h"
  #+end_src

* Context

  The following arrays are stored in the context:

  |--------------------+---------------+----------------------------------------------------------------------|
  | ~type~             |               | Gaussian (~'G'~) or Slater (~'S'~)                                   |
  | ~shell_num~        |               | Number of shells                                                     |
  | ~prim_num~         |               | Total number of primitives                                           |
  | ~nucleus_index~    | ~[nucl_num]~  | Index of the first shell of each nucleus                             |
  | ~shell_ang_mom~    | ~[shell_num]~ | Angular momentum of each shell                                       |
  | ~shell_prim_num~   | ~[shell_num]~ | Number of primitives in each shell                                   |
  | ~shell_prim_index~ | ~[shell_num]~ | Address of the first primitive of each shell in the ~EXPONENT~ array |
  | ~shell_factor~     | ~[shell_num]~ | Normalization factor for each shell                                  |
  | ~exponent~         | ~[prim_num]~  | Array of exponents                                                   |
  | ~coefficient~      | ~[prim_num]~  | Array of coefficients                                                |
  | ~prim_factor~      | ~[prim_num]~  | Normalization factors of the primtives                               |

  Computed data:
  
  |----------------------+-------------------------------------+-----------------------------------------------------------------------------------------------|
  | ~nucleus_prim_index~ | ~[nucl_num]~                        | Index of the first primitive for each nucleus                                                 |
  | ~primitive_vgl~      | ~[prim_num][5][walk_num][elec_num]~ | Value, gradients, Laplacian of the primitives at electron positions                           |
  | ~primitive_vgl_date~ | ~uint64_t~                          | Late modification date of Value, gradients, Laplacian of the primitives at electron positions |
  | ~shell_vgl~          | ~[prim_num][5][walk_num][elec_num]~ | Value, gradients, Laplacian of the primitives at electron positions                           |
  | ~shell_vgl_date~     | ~uint64_t~                          | Late modification date of Value, gradients, Laplacian of the shells at electron positions     |
  |----------------------+-------------------------------------+-----------------------------------------------------------------------------------------------|
  | ~nucl_shell_index~   | ~[nucl_num]~                        | Index of the first shell for each nucleus                                                     |
  | ~exponent_sorted~    | ~[prim_num]~                        | Array of exponents for sorted primitives                                                      |
  | ~coeff_norm_sorted~  | ~[prim_num]~                        | Array of normalized coefficients for sorted primitives                                        |
  | ~prim_factor_sorted~ | ~[prim_num]~                        | Normalization factors of the sorted primtives                                                 |
  | ~nuclear_radius~     | ~[nucl_num]~                        | Distance beyond which all the AOs are zero                                                    |

   For H_2 with the following basis set,

   #+BEGIN_EXAMPLE
HYDROGEN
S   5
1         3.387000E+01           6.068000E-03
2         5.095000E+00           4.530800E-02
3         1.159000E+00           2.028220E-01
4         3.258000E-01           5.039030E-01
5         1.027000E-01           3.834210E-01
S   1
1         3.258000E-01           1.000000E+00
S   1
1         1.027000E-01           1.000000E+00
P   1
1         1.407000E+00           1.000000E+00
P   1
1         3.880000E-01           1.000000E+00
D   1
1         1.057000E+00           1.0000000
   #+END_EXAMPLE

   we have:

   #+BEGIN_EXAMPLE
type = 'G'
shell_num = 12
prim_num = 20
nucleus_index = [0 , 6]
shell_ang_mom = [0, 0, 0, 1, 1, 2, 0, 0, 0, 1, 1, 2]
shell_factor  = [ 1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.,  1.]
shell_prim_num = [5, 1, 1, 1, 1, 1, 5, 1, 1, 1, 1, 1]
shell_prim_index = [0 , 5 , 6 , 7 , 8 , 9 , 10, 15, 16, 17, 18, 19]
exponent = [ 33.87, 5.095, 1.159, 0.3258, 0.1027, 0.3258, 0.1027, 1.407,
  0.388, 1.057, 33.87, 5.095, 1.159, 0.3258, 0.1027, 0.3258, 0.1027, 1.407,
  0.388, 1.057]
coefficient = [ 0.006068, 0.045308, 0.202822, 0.503903, 0.383421, 1.0, 1.0,
  1.0, 1.0, 1.0, 0.006068, 0.045308, 0.202822, 0.503903, 0.383421, 1.0, 1.0,
  1.0, 1.0, 1.0]
prim_factor = [ 1.0006253235944540e+01, 2.4169531573445120e+00, 7.9610924849766440e-01
  3.0734305383061117e-01, 1.2929684417481876e-01, 3.0734305383061117e-01,
  1.2929684417481876e-01, 2.1842769845268308e+00, 4.3649547399719840e-01,
  1.8135965626177861e+00, 1.0006253235944540e+01, 2.4169531573445120e+00,
  7.9610924849766440e-01, 3.0734305383061117e-01, 1.2929684417481876e-01,
  3.0734305383061117e-01, 1.2929684417481876e-01, 2.1842769845268308e+00,
  4.3649547399719840e-01, 1.8135965626177861e+00 ]
   #+END_EXAMPLE

** Data structure

   #+begin_src c :comments org :tangle (eval h_private_type)
typedef struct qmckl_ao_basis_struct {
  int32_t   uninitialized;
  int64_t   shell_num;
  int64_t   prim_num;
  int64_t * nucleus_index;
  int64_t * nucleus_shell_num;
  int32_t * shell_ang_mom;
  int64_t * shell_prim_num;
  int64_t * nucleus_prim_index;
  int64_t * shell_prim_index;
  double  * shell_factor;
  double  * exponent    ;
  double  * coefficient ;
  double  * prim_factor ;
  double  * primitive_vgl;
  int64_t   primitive_vgl_date;
  double  * shell_vgl;
  int64_t   shell_vgl_date;
  bool      provided;
  char      type;
} qmckl_ao_basis_struct;
   #+end_src

   The ~uninitialized~ integer contains one bit set to one for each
   initialization function which has not been called. It becomes equal
   to zero after all initialization functions have been called. The
   struct is then initialized and ~provided == true~.
   Some values are initialized by default, and are not concerned by
   this mechanism.

   #+begin_src c :comments org :tangle (eval h_private_func) 
qmckl_exit_code qmckl_init_ao_basis(qmckl_context context);
   #+end_src
   
   #+begin_src c :comments org :tangle (eval c)
qmckl_exit_code qmckl_init_ao_basis(qmckl_context context) {

  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return false;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  ctx->ao_basis.uninitialized = (1 << 12) - 1;

 /* Default values */
  /* ctx->ao_basis.
     ,*/

  return QMCKL_SUCCESS;
}
   #+end_src
   
** Access functions

   #+begin_src c :comments org :tangle (eval h_private_func) :exports none
char      qmckl_get_ao_basis_type             (const qmckl_context context);
int64_t   qmckl_get_ao_basis_shell_num        (const qmckl_context context);
int64_t   qmckl_get_ao_basis_prim_num         (const qmckl_context context);
int64_t*  qmckl_get_ao_basis_nucleus_index    (const qmckl_context context);
int32_t*  qmckl_get_ao_basis_shell_ang_mom    (const qmckl_context context);
int64_t*  qmckl_get_ao_basis_shell_prim_num   (const qmckl_context context);
int64_t*  qmckl_get_ao_basis_shell_prim_index (const qmckl_context context);
double*   qmckl_get_ao_basis_shell_factor     (const qmckl_context context);
double*   qmckl_get_ao_basis_exponent         (const qmckl_context context);
double*   qmckl_get_ao_basis_coefficient      (const qmckl_context context);
double*   qmckl_get_ao_basis_prim_factor      (const qmckl_context context);
   #+end_src

   When all the data for the AOs have been provided, the following
   function returns ~true~.

   #+begin_src c :comments org :tangle (eval h_func)
bool      qmckl_ao_basis_provided           (const qmckl_context context);
   #+end_src

   #+NAME:post
   #+begin_src c :exports none
if ( (ctx->ao_basis.uninitialized & mask) != 0) {
  return NULL;
}
   #+end_src

   #+begin_src c :comments org :tangle (eval c) :noweb yes :exports none
char qmckl_get_ao_basis_type (const qmckl_context context) {

  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return (char) 0;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return (char) 0;
  }

  assert (ctx->ao_basis.type != (char) 0);
  return ctx->ao_basis.type;
}


int64_t qmckl_get_ao_basis_shell_num (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return (int64_t) 0;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 1;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return (int64_t) 0;
  }

  assert (ctx->ao_basis.shell_num > (int64_t) 0);
  return ctx->ao_basis.shell_num;
}


int64_t qmckl_get_ao_basis_prim_num (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return (int64_t) 0;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 2;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return (int64_t) 0;
  }

  assert (ctx->ao_basis.prim_num > (int64_t) 0);
  return ctx->ao_basis.prim_num;
}


int64_t* qmckl_get_ao_basis_nucleus_shell_num (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return NULL;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 3;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return NULL;
  }

  assert (ctx->ao_basis.nucleus_shell_num != NULL);
  return ctx->ao_basis.nucleus_shell_num ;
}

int64_t* qmckl_get_ao_basis_nucleus_index (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return NULL;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 4;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return NULL;
  }

  assert (ctx->ao_basis.nucleus_index != NULL);
  return ctx->ao_basis.nucleus_index ;
}


int32_t* qmckl_get_ao_basis_shell_ang_mom (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return NULL;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 5;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return NULL;
  }

  assert (ctx->ao_basis.shell_ang_mom != NULL);
  return ctx->ao_basis.shell_ang_mom;
}


int64_t* qmckl_get_ao_basis_shell_prim_num (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return NULL;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 6;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return NULL;
  }

  assert (ctx->ao_basis.shell_prim_num != NULL);
  return ctx->ao_basis.shell_prim_num;
}


int64_t* qmckl_get_ao_basis_shell_prim_index (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return NULL;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 7;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return NULL;
  }

  assert (ctx->ao_basis.shell_prim_index != NULL);
  return ctx->ao_basis.shell_prim_index;
}


double* qmckl_get_ao_basis_shell_factor (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return NULL;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 8;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return NULL;
  }

  assert (ctx->ao_basis.shell_factor != NULL);
  return ctx->ao_basis.shell_factor;
}


double* qmckl_get_ao_basis_exponent (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return NULL;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);


  int32_t mask = 1 << 9;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return NULL;
  }

  assert (ctx->ao_basis.exponent != NULL);
  return ctx->ao_basis.exponent;
}


double* qmckl_get_ao_basis_coefficient (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return NULL;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 10;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return NULL;
  }

  assert (ctx->ao_basis.coefficient != NULL);
  return ctx->ao_basis.coefficient;
}


double* qmckl_get_ao_basis_prim_factor (const qmckl_context context) {
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return NULL;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int32_t mask = 1 << 11;

  if ( (ctx->ao_basis.uninitialized & mask) != 0) {
    return NULL;
  }

  assert (ctx->ao_basis.prim_factor != NULL);
  return ctx->ao_basis.prim_factor;
}


bool qmckl_ao_basis_provided(const qmckl_context context) {

  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return false;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  return ctx->ao_basis.provided;
}
   #+end_src

** Initialization functions

   To set the basis set, all the following functions need to be
   called.

   #+begin_src c :comments org :tangle (eval h_func)
qmckl_exit_code  qmckl_set_ao_basis_type             (qmckl_context context, const char      t);
qmckl_exit_code  qmckl_set_ao_basis_shell_num        (qmckl_context context, const int64_t   shell_num);
qmckl_exit_code  qmckl_set_ao_basis_prim_num         (qmckl_context context, const int64_t   prim_num);
qmckl_exit_code  qmckl_set_ao_basis_nucleus_index    (qmckl_context context, const int64_t * nucleus_index);
qmckl_exit_code  qmckl_set_ao_basis_nucleus_shell_num(qmckl_context context, const int64_t * nucleus_shell_num);
qmckl_exit_code  qmckl_set_ao_basis_shell_ang_mom    (qmckl_context context, const int32_t * shell_ang_mom);
qmckl_exit_code  qmckl_set_ao_basis_shell_prim_num   (qmckl_context context, const int64_t * shell_prim_num);
qmckl_exit_code  qmckl_set_ao_basis_shell_prim_index (qmckl_context context, const int64_t * shell_prim_index);
qmckl_exit_code  qmckl_set_ao_basis_shell_factor     (qmckl_context context, const double  * shell_factor);
qmckl_exit_code  qmckl_set_ao_basis_exponent         (qmckl_context context, const double  * exponent);
qmckl_exit_code  qmckl_set_ao_basis_coefficient      (qmckl_context context, const double  * coefficient);
qmckl_exit_code  qmckl_set_ao_basis_prim_factor      (qmckl_context context, const double  * prim_factor);
   #+end_src

   #+NAME:pre2
   #+begin_src c  :exports none
if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
  return QMCKL_NULL_CONTEXT;
 }

qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
   #+end_src

   #+NAME:post2
   #+begin_src c  :exports none
ctx->ao_basis.uninitialized &= ~mask;
ctx->ao_basis.provided = (ctx->ao_basis.uninitialized == 0);
if (ctx->ao_basis.provided) {
  qmckl_exit_code rc_ = qmckl_finalize_basis(context);
  if (rc_ != QMCKL_SUCCESS) return rc_;
 }

return QMCKL_SUCCESS;
   #+end_src

   #+begin_src c :comments org :tangle (eval c) :noweb yes :exports none
qmckl_exit_code qmckl_set_ao_basis_type(qmckl_context context, const char t) {
  <<pre2>>

  if (t != 'G' && t != 'S') {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_set_ao_basis_type",
                           NULL);
  }

  int32_t mask = 1;
  ctx->ao_basis.type = t;

  <<post2>>
}


qmckl_exit_code qmckl_set_ao_basis_shell_num(qmckl_context context, const int64_t shell_num) {
  <<pre2>>

  if (shell_num <= 0) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_set_ao_basis_shell_num",
                           "shell_num <= 0");
  }

  int64_t prim_num = qmckl_get_ao_basis_prim_num(context);

  if (0L < prim_num && prim_num < shell_num) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_set_ao_basis_shell_num",
                           "shell_num > prim_num");
  }

  int32_t mask = 1 << 1;
  ctx->ao_basis.shell_num = shell_num;

  <<post2>>
}


qmckl_exit_code  qmckl_set_ao_basis_prim_num(qmckl_context context, const int64_t prim_num) {
  <<pre2>>

  if (prim_num <= 0) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_set_ao_basis_shell_num",
                           "prim_num must be positive");
  }

  int64_t shell_num = qmckl_get_ao_basis_shell_num(context);

  if (prim_num < shell_num) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_set_ao_basis_shell_num",
                           "prim_num < shell_num");
  }

  int32_t mask = 1 << 2;
  ctx->ao_basis.prim_num = prim_num;

  <<post2>>
}


qmckl_exit_code  qmckl_set_ao_basis_nucleus_shell_num(qmckl_context context, const int64_t* nucleus_shell_num) {
  <<pre2>>

  int32_t mask = 1 << 3;

  const int64_t shell_num = qmckl_get_ao_basis_shell_num(context);
  if (shell_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_ao_basis_nucleus_shell_num",
                           "shell_num is not set");
  }

  if (ctx->ao_basis.nucleus_shell_num != NULL) {
    qmckl_exit_code rc = qmckl_free(context, ctx->ao_basis.nucleus_shell_num);
    if (rc != QMCKL_SUCCESS) {
      return qmckl_failwith( context, rc,
                             "qmckl_set_ao_basis_nucleus_shell_num",
                             NULL);
    }
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = shell_num * sizeof(int64_t);
  int64_t* new_array = (int64_t*) qmckl_malloc(context, mem_info);

  if (new_array == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_ao_basis_nucleus_shell_num",
                           NULL);
  }

  memcpy(new_array, nucleus_shell_num, mem_info.size);

  ctx->ao_basis.nucleus_shell_num = new_array;

  <<post2>>
}

qmckl_exit_code  qmckl_set_ao_basis_nucleus_index(qmckl_context context, const int64_t* nucleus_index) {
  <<pre2>>

  int32_t mask = 1 << 4;

  const int64_t shell_num = qmckl_get_ao_basis_shell_num(context);
  if (shell_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_ao_basis_nucleus_index",
                           "shell_num is not set");
  }

  if (ctx->ao_basis.nucleus_index != NULL) {
    qmckl_exit_code rc = qmckl_free(context, ctx->ao_basis.nucleus_index);
    if (rc != QMCKL_SUCCESS) {
      return qmckl_failwith( context, rc,
                             "qmckl_set_ao_basis_nucleus_index",
                             NULL);
    }
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = shell_num * sizeof(int64_t);
  int64_t* new_array = (int64_t*) qmckl_malloc(context, mem_info);

  if (new_array == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_ao_basis_nucleus_index",
                           NULL);
  }

  memcpy(new_array, nucleus_index, mem_info.size);

  ctx->ao_basis.nucleus_index = new_array;

  <<post2>>
}


qmckl_exit_code  qmckl_set_ao_basis_shell_ang_mom(qmckl_context context, const int32_t* shell_ang_mom) {
  <<pre2>>

  int32_t mask = 1 << 5;

  const int64_t shell_num = qmckl_get_ao_basis_shell_num(context);
  if (shell_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_ao_basis_shell_ang_mom",
                           "shell_num is not set");
  }

  if (ctx->ao_basis.shell_ang_mom != NULL) {
    qmckl_exit_code rc = qmckl_free(context, ctx->ao_basis.shell_ang_mom);
    if (rc != QMCKL_SUCCESS) {
      return qmckl_failwith( context, rc,
                             "qmckl_set_ao_basis_shell_ang_mom",
                             NULL);
    }
  }


  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = shell_num * sizeof(char);
  int32_t * new_array = (int32_t*) qmckl_malloc(context, mem_info);

  if (new_array == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_ao_basis_shell_ang_mom",
                           NULL);
  }

  memcpy(new_array, shell_ang_mom, mem_info.size);

  ctx->ao_basis.shell_ang_mom = new_array;

  <<post2>>
}


qmckl_exit_code  qmckl_set_ao_basis_shell_prim_num(qmckl_context context, const int64_t* shell_prim_num) {
  <<pre2>>

  int32_t mask = 1 << 6;

  const int64_t shell_num = qmckl_get_ao_basis_shell_num(context);
  if (shell_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_ao_basis_shell_prim_num",
                           "shell_num is not set");
  }

  if (ctx->ao_basis.shell_prim_num != NULL) {
    qmckl_exit_code rc = qmckl_free(context, ctx->ao_basis.shell_prim_num);
    if (rc != QMCKL_SUCCESS) {
      return qmckl_failwith( context, rc,
                             "qmckl_set_ao_basis_shell_prim_num",
                             NULL);
    }
  }


  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = shell_num * sizeof(int64_t);
  int64_t* new_array = (int64_t*) qmckl_malloc(context, mem_info);

  if (new_array == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_ao_basis_shell_prim_num",
                           NULL);
  }

  memcpy(new_array, shell_prim_num, mem_info.size);

  ctx->ao_basis.shell_prim_num = new_array;

  <<post2>>
}


qmckl_exit_code  qmckl_set_ao_basis_shell_prim_index(qmckl_context context, const int64_t* shell_prim_index) {
  <<pre2>>

  int32_t mask = 1 << 7;

  const int64_t shell_num = qmckl_get_ao_basis_shell_num(context);
  if (shell_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_ao_basis_shell_prim_index",
                           "shell_num is not set");
  }

  if (ctx->ao_basis.shell_prim_index != NULL) {
    qmckl_exit_code rc = qmckl_free(context, ctx->ao_basis.shell_prim_index);
    if (rc != QMCKL_SUCCESS) {
      return qmckl_failwith( context, rc,
                             "qmckl_set_ao_basis_shell_prim_index",
                             NULL);
    }
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = shell_num * sizeof(int64_t);
  int64_t* new_array = (int64_t*) qmckl_malloc(context, mem_info);

  if (new_array == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_ao_basis_shell_prim_index",
                           NULL);
  }

  memcpy(new_array, shell_prim_index, mem_info.size);

  ctx->ao_basis.shell_prim_index = new_array;

  <<post2>>
}


qmckl_exit_code  qmckl_set_ao_basis_shell_factor(qmckl_context context, const double* shell_factor) {
  <<pre2>>

  int32_t mask = 1 << 8;

  const int64_t shell_num = qmckl_get_ao_basis_shell_num(context);
  if (shell_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_ao_basis_shell_factor",
                           "shell_num is not set");
  }


  if (ctx->ao_basis.shell_factor != NULL) {
    qmckl_exit_code rc = qmckl_free(context, ctx->ao_basis.shell_factor);
    if (rc != QMCKL_SUCCESS) {
      return qmckl_failwith( context, rc,
                             "qmckl_set_ao_basis_shell_factor",
                             NULL);
    }
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = shell_num * sizeof(double);
  double* new_array = (double*) qmckl_malloc(context, mem_info);

  if (new_array == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_ao_basis_shell_factor",
                           NULL);
  }

  memcpy(new_array, shell_factor, mem_info.size);

  ctx->ao_basis.shell_factor = new_array;

  <<post2>>
}

qmckl_exit_code  qmckl_set_ao_basis_exponent(qmckl_context context, const double* exponent) {
  <<pre2>>

  int32_t mask = 1 << 9;

  const int64_t prim_num = qmckl_get_ao_basis_prim_num(context);
  if (prim_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_ao_basis_exponent",
                           "prim_num is not set");
  }

  if (ctx->ao_basis.exponent != NULL) {
    qmckl_exit_code rc = qmckl_free(context, ctx->ao_basis.exponent);
    if (rc != QMCKL_SUCCESS) {
      return qmckl_failwith( context, rc,
                             "qmckl_set_ao_basis_exponent",
                             NULL);
    }
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = prim_num * sizeof(double);
  double* new_array = (double*) qmckl_malloc(context, mem_info);

  if (new_array == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_ao_basis_exponent",
                           NULL);
  }

  memcpy(new_array, exponent, mem_info.size);

  ctx->ao_basis.exponent = new_array;

  <<post2>>
}

qmckl_exit_code  qmckl_set_ao_basis_coefficient(qmckl_context context, const double* coefficient) {
  <<pre2>>

  int32_t mask = 1 << 10;

  const int64_t prim_num = qmckl_get_ao_basis_prim_num(context);
  if (prim_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_ao_basis_coefficient",
                           "prim_num is not set");
  }

  if (ctx->ao_basis.coefficient != NULL) {
    qmckl_exit_code rc = qmckl_free(context, ctx->ao_basis.coefficient);
    if (rc != QMCKL_SUCCESS) {
      return qmckl_failwith( context, rc,
                             "qmckl_set_ao_basis_coefficient",
                             NULL);
    }
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = prim_num * sizeof(double);
  double* new_array = (double*) qmckl_malloc(context, mem_info);

  if (new_array == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_ao_basis_coefficient",
                           NULL);
  }

  memcpy(new_array, coefficient, mem_info.size);

  ctx->ao_basis.coefficient = new_array;

  <<post2>>
}

qmckl_exit_code  qmckl_set_ao_basis_prim_factor(qmckl_context context, const double* prim_factor) {
  <<pre2>>

  int32_t mask = 1 << 11;

  const int64_t prim_num = qmckl_get_ao_basis_prim_num(context);
  if (prim_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_ao_basis_prim_factor",
                           "prim_num is not set");
  }


  if (ctx->ao_basis.prim_factor != NULL) {
    qmckl_exit_code rc = qmckl_free(context, ctx->ao_basis.prim_factor);
    if (rc != QMCKL_SUCCESS) {
      return qmckl_failwith( context, rc,
                             "qmckl_set_ao_basis_prim_factor",
                             NULL);
    }
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = prim_num * sizeof(double);
  double* new_array = (double*) qmckl_malloc(context, mem_info);

  if (new_array == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_ao_basis_prim_factor",
                           NULL);
  }

  memcpy(new_array, prim_factor, mem_info.size);

  ctx->ao_basis.prim_factor = new_array;

  <<post2>>
}

   #+end_src

 When the basis set is completely entered, other data structures are
 computed to accelerate the calculations. The primitives within each
 contraction are sorted in ascending order of their exponents, such
 that as soon as a primitive is zero all the following functions
 vanish. Also, it is possible to compute a nuclear radius beyond which
 all the primitives are zero up to the numerical accuracy defined in
 the context.

   #+begin_src c :comments org :tangle (eval h_private_func) :noweb yes :exports none
qmckl_exit_code qmckl_finalize_basis(qmckl_context context);
   #+end_src

   #+begin_src c :comments org :tangle (eval c) :noweb yes :exports none
qmckl_exit_code qmckl_finalize_basis(qmckl_context context) {

  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return QMCKL_INVALID_CONTEXT;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  int64_t nucl_num = 0;
  qmckl_exit_code rc = QMCKL_FAILURE;

  rc = qmckl_get_nucleus_num(context, &nucl_num);
  if (rc != QMCKL_SUCCESS) return rc;

 /* nucleus_prim_index */
  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = (ctx->nucleus.num + (int64_t) 1) * sizeof(int64_t);

  ctx->ao_basis.nucleus_prim_index = (int64_t*) qmckl_malloc(context, mem_info);

  if (ctx->ao_basis.nucleus_prim_index == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_nucleus_prim_index",
                           NULL);
  }

  for (int64_t i=0 ; i<nucl_num ; ++i) {
    int64_t shell_idx = ctx->ao_basis.nucleus_index[i];
    ctx->ao_basis.nucleus_prim_index[i] = ctx->ao_basis.shell_prim_index[shell_idx];
  }
  ctx->ao_basis.nucleus_prim_index[nucl_num] = ctx->ao_basis.prim_num;
  

 /* TODO : sort the basis set here */
  return QMCKL_SUCCESS;
}
   #+end_src
   
** Fortran interfaces

    #+begin_src f90 :tangle (eval fh_func) :comments org :exports none                       
interface
  integer(c_int32_t) function qmckl_set_ao_basis_type (context, t) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    character(c_char)   , intent(in)  , value :: t
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_shell_num(context, num) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    integer (c_int64_t) , intent(in)  , value :: num
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_prim_num(context, num) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    integer (c_int64_t) , intent(in)  , value :: num
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_nucleus_index(context, idx) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    integer (c_int64_t) , intent(in)          :: idx(*)
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_nucleus_shell_num(context,shell_num) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    integer (c_int64_t) , intent(in)          :: shell_num(*)
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_nucleus_shell_ang_mom(context,shell_ang_mom) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    integer (c_int32_t) , intent(in)          :: shell_ang_mom(*)
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_nucleus_shell_prim_num(context,shell_prim_num) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    integer (c_int64_t) , intent(in)          :: shell_prim_num(*)
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_nucleus_shell_prim_index(context,shell_prim_index) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    integer (c_int64_t) , intent(in)          :: shell_prim_index(*)
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_nucleus_shell_factor(context,shell_factor) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    real    (c_double)  , intent(in)          :: shell_factor(*)
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_nucleus_exponent(context,exponent) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    real    (c_double)  , intent(in)          :: exponent(*)
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_nucleus_coefficient(context,coefficient) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    real    (c_double)  , intent(in)          :: coefficient(*)
  end function
end interface
interface
  integer(c_int32_t) function qmckl_set_ao_basis_nucleus_prim_factor(context,prim_factor) &
    bind(C)
    use, intrinsic :: iso_c_binding
    import
    implicit none
    integer (c_int64_t) , intent(in)  , value :: context
    real    (c_double)  , intent(in)          :: prim_factor(*)
  end function
end interface
   #+end_src

** Test                                                            :noexport:

   #+begin_src c :tangle (eval c_test) :exports none :exports none
const int64_t   nucl_num      = chbrclf_nucl_num;
const double*   nucl_charge   = chbrclf_charge;
const double*   nucl_coord    = &(chbrclf_nucl_coord[0][0]);

qmckl_exit_code rc;
rc = qmckl_set_nucleus_num (context, nucl_num);
assert(rc == QMCKL_SUCCESS);

rc = qmckl_set_nucleus_coord (context, 'T', &(nucl_coord[0]));
assert(rc == QMCKL_SUCCESS);

rc = qmckl_set_nucleus_charge(context, nucl_charge);
assert(rc == QMCKL_SUCCESS);

assert(qmckl_nucleus_provided(context));


const int64_t    shell_num         = chbrclf_shell_num;
const int64_t    prim_num          = chbrclf_prim_num;
const int64_t *  nucleus_index     =  &(chbrclf_basis_nucleus_index[0]);
const int64_t *  nucleus_shell_num =  &(chbrclf_basis_nucleus_shell_num[0]);
const int32_t *  shell_ang_mom     =  &(chbrclf_basis_shell_ang_mom[0]);
const int64_t *  shell_prim_num    =  &(chbrclf_basis_shell_prim_num[0]);
const int64_t *  shell_prim_index  =  &(chbrclf_basis_shell_prim_index[0]);
const double  *  shell_factor      =  &(chbrclf_basis_shell_factor[0]);
const double  *  exponent          =  &(chbrclf_basis_exponent[0]);
const double  *  coefficient       =  &(chbrclf_basis_coefficient[0]);
const double  *  prim_factor       =  &(chbrclf_basis_prim_factor[0]);

char    typ = 'G';

assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_type (context, typ);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_shell_num (context, shell_num);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_prim_num (context, prim_num);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_nucleus_index (context, nucleus_index);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_nucleus_shell_num (context, nucleus_shell_num);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_shell_ang_mom (context, shell_ang_mom);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_shell_factor  (context, shell_factor);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_shell_prim_num (context, shell_prim_num);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_shell_prim_index (context, shell_prim_index);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_exponent      (context, exponent);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_coefficient   (context, coefficient);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_ao_basis_provided(context));

rc = qmckl_set_ao_basis_prim_factor (context, prim_factor);
assert(rc == QMCKL_SUCCESS);
assert(qmckl_ao_basis_provided(context));

   #+end_src
   
* Radial part
** General functions for Gaussian basis functions

 ~qmckl_ao_gaussian_vgl~ computes the values, gradients and
    Laplacians at a given point of ~n~ Gaussian functions centered at
    the same point:

    \[ v_i = \exp(-a_i |X-R|^2) \]
    \[ \nabla_x v_i = -2 a_i (X_x -  R_x) v_i \]
    \[ \nabla_y v_i = -2 a_i (X_y -  R_y) v_i \]
    \[ \nabla_z v_i = -2 a_i (X_z -  R_z) v_i \]
    \[ \Delta v_i = a_i (4 |X-R|^2 a_i - 6) v_i \]

     |--------------+--------+------------------------------------------------------|
     | ~context~    | input  | Global state                                         |
     | ~X(3)~       | input  | Array containing the coordinates of the points       |
     | ~R(3)~       | input  | Array containing the x,y,z coordinates of the center |
     | ~n~          | input  | Number of computed Gaussians                         |
     | ~A(n)~       | input  | Exponents of the Gaussians                           |
     | ~VGL(ldv,5)~ | output | Value, gradients and Laplacian of the Gaussians      |
     | ~ldv~        | input  | Leading dimension of array ~VGL~                     |
     |--------------+--------+------------------------------------------------------|

     Requirements

     - ~context~ is not 0
     - ~n~ > 0
     - ~ldv~ >= 5
     - ~A(i)~ > 0 for all ~i~
     - ~X~ is allocated with at least $3 \times 8$ bytes
     - ~R~ is allocated with at least $3 \times 8$ bytes
     - ~A~ is allocated with at least $n \times 8$ bytes
     - ~VGL~ is allocated with at least $n \times 5 \times 8$ bytes

     #+begin_src c :tangle (eval h_func)
qmckl_exit_code
qmckl_ao_gaussian_vgl(const qmckl_context context,
                      const double *X,
                      const double *R,
                      const int64_t *n,
                      const int64_t *A,
                      const double *VGL,
                      const int64_t ldv);
     #+end_src

     #+begin_src f90 :tangle (eval f)
integer function qmckl_ao_gaussian_vgl_f(context, X, R, n, A, VGL, ldv) result(info)
  use qmckl
  implicit none
  integer*8 , intent(in)  :: context
  real*8    , intent(in)  :: X(3), R(3)
  integer*8 , intent(in)  :: n
  real*8    , intent(in)  :: A(n)
  real*8    , intent(out) :: VGL(ldv,5)
  integer*8 , intent(in)  :: ldv

  integer*8         :: i,j
  real*8            :: Y(3), r2, t, u, v

  info = QMCKL_SUCCESS

  if (context == QMCKL_NULL_CONTEXT) then
     info = QMCKL_INVALID_CONTEXT
     return
  endif

  if (n <= 0) then
     info = QMCKL_INVALID_ARG_4
     return
  endif

  if (ldv < n) then
     info = QMCKL_INVALID_ARG_7
     return
  endif


  do i=1,3
     Y(i) = X(i) - R(i)
  end do
  r2 = Y(1)*Y(1) + Y(2)*Y(2) + Y(3)*Y(3)

  do i=1,n
     VGL(i,1) = dexp(-A(i) * r2)
  end do

  do i=1,n
     VGL(i,5) = A(i) * VGL(i,1)
  end do

  t = -2.d0 * ( X(1) - R(1) )
  u = -2.d0 * ( X(2) - R(2) )
  v = -2.d0 * ( X(3) - R(3) )

  do i=1,n
     VGL(i,2) = t * VGL(i,5)
     VGL(i,3) = u * VGL(i,5)
     VGL(i,4) = v * VGL(i,5)
  end do

  t = 4.d0 * r2
  do i=1,n
     VGL(i,5) = (t * A(i) - 6.d0) *  VGL(i,5)
  end do

end function qmckl_ao_gaussian_vgl_f
     #+end_src

     #+begin_src f90 :tangle (eval f) :exports none
integer(c_int32_t) function qmckl_ao_gaussian_vgl(context, X, R, n, A, VGL, ldv) &
     bind(C) result(info)
  use, intrinsic :: iso_c_binding
  implicit none
  integer (c_int64_t) , intent(in) , value :: context
  real    (c_double)  , intent(in)         :: X(3), R(3)
  integer (c_int64_t) , intent(in) , value :: n
  real    (c_double)  , intent(in)         :: A(n)
  real    (c_double)  , intent(out)        :: VGL(ldv,5)
  integer (c_int64_t) , intent(in) , value :: ldv

  integer, external :: qmckl_ao_gaussian_vgl_f
  info = qmckl_ao_gaussian_vgl_f(context, X, R, n, A, VGL, ldv)
end function qmckl_ao_gaussian_vgl
     #+end_src

     #+begin_src f90 :tangle (eval fh_func) :exports none
  interface
     integer(c_int32_t) function qmckl_ao_gaussian_vgl(context, X, R, n, A, VGL, ldv) &
          bind(C)
       use, intrinsic :: iso_c_binding
       integer (c_int64_t) , intent(in) , value :: context
       integer (c_int64_t) , intent(in) , value :: ldv
       integer (c_int64_t) , intent(in) , value :: n
       real    (c_double)  , intent(in)         :: X(3), R(3), A(n)
       real    (c_double)  , intent(out)        :: VGL(ldv,5)
     end function qmckl_ao_gaussian_vgl
  end interface
     #+end_src

   # Test
   #+begin_src f90 :tangle (eval f_test)
integer(c_int32_t) function test_qmckl_ao_gaussian_vgl(context) bind(C)
  use qmckl
  implicit none

  integer(c_int64_t), intent(in), value :: context

  integer*8                     :: n, ldv, j, i
  double precision              :: X(3), R(3), Y(3), r2
  double precision, allocatable :: VGL(:,:), A(:)
  double precision              :: epsilon

  epsilon = qmckl_get_numprec_epsilon(context)

  X = (/ 1.1 , 2.2 ,  3.3 /)
  R = (/ 0.1 , 1.2 , -2.3 /)
  Y(:) = X(:) - R(:)
  r2 = Y(1)**2 + Y(2)**2 + Y(3)**2

  n = 10;
  ldv = 100;

  allocate (A(n), VGL(ldv,5))
  do i=1,n
     A(i) = 0.0013 * dble(ishft(1,i))
  end do


  test_qmckl_ao_gaussian_vgl = &
       qmckl_ao_gaussian_vgl(context, X, R, n, A, VGL, ldv)
  if (test_qmckl_ao_gaussian_vgl /= 0) return

  test_qmckl_ao_gaussian_vgl = -1

  do i=1,n
     test_qmckl_ao_gaussian_vgl = -11
     if (dabs(1.d0 - VGL(i,1) / (&
          dexp(-A(i) * r2) &
          )) > epsilon ) return

     test_qmckl_ao_gaussian_vgl = -12
     if (dabs(1.d0 - VGL(i,2) / (&
          -2.d0 * A(i) * Y(1) * dexp(-A(i) * r2) &
          )) > epsilon ) return

     test_qmckl_ao_gaussian_vgl = -13
     if (dabs(1.d0 - VGL(i,3) / (&
          -2.d0 * A(i) * Y(2) * dexp(-A(i) * r2) &
          )) > epsilon ) return

     test_qmckl_ao_gaussian_vgl = -14
     if (dabs(1.d0 - VGL(i,4) / (&
          -2.d0 * A(i) * Y(3) * dexp(-A(i) * r2) &
          )) > epsilon ) return

     test_qmckl_ao_gaussian_vgl = -15
     if (dabs(1.d0 - VGL(i,5) / (&
          A(i) * (4.d0*r2*A(i) - 6.d0) * dexp(-A(i) * r2) &
          )) > epsilon ) return
  end do

  test_qmckl_ao_gaussian_vgl = 0

  deallocate(VGL)
end function test_qmckl_ao_gaussian_vgl
   #+end_src

   #+begin_src c :tangle (eval c_test) :exports none
    int test_qmckl_ao_gaussian_vgl(qmckl_context context);
    assert(0 == test_qmckl_ao_gaussian_vgl(context));
   #+end_src

** TODO General functions for Slater basis functions
** TODO General functions for Radial functions on a grid
** DONE Computation of primitives

*** Get

    #+begin_src c :comments org :tangle (eval h_func) :noweb yes
qmckl_exit_code qmckl_get_ao_basis_primitive_vgl(qmckl_context context, double* const primitive_vgl);
    #+end_src

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_get_ao_basis_primitive_vgl(qmckl_context context, double* const primitive_vgl) {
  
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return QMCKL_NULL_CONTEXT;
  }

  qmckl_exit_code rc;

  rc = qmckl_provide_ao_basis_primitive_vgl(context);
  if (rc != QMCKL_SUCCESS) return rc;

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  size_t sze = ctx->ao_basis.prim_num * 5 * ctx->electron.num * ctx->electron.walk_num;
  memcpy(primitive_vgl, ctx->ao_basis.primitive_vgl, sze * sizeof(double));

  return QMCKL_SUCCESS;
}
    #+end_src

*** Provide

    #+begin_src c :comments org :tangle (eval h_private_func) :noweb yes :exports none
qmckl_exit_code qmckl_provide_ao_basis_primitive_vgl(qmckl_context context);
    #+end_src

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_provide_ao_basis_primitive_vgl(qmckl_context context)
{

  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return QMCKL_NULL_CONTEXT;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  if (!ctx->ao_basis.provided) {
    return qmckl_failwith( context,
                           QMCKL_NOT_PROVIDED,
                           "qmckl_ao_basis_primitive_vgl",
                           NULL);
  }
  
 /* Compute if necessary */
  if (ctx->electron.coord_new_date > ctx->ao_basis.primitive_vgl_date) {

 /* Allocate array */
    if (ctx->ao_basis.primitive_vgl == NULL) {

      qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
      mem_info.size = ctx->ao_basis.prim_num * 5 * ctx->electron.num *
        ctx->electron.walk_num * sizeof(double);
      double* primitive_vgl = (double*) qmckl_malloc(context, mem_info);

      if (primitive_vgl == NULL) {
        return qmckl_failwith( context,
                               QMCKL_ALLOCATION_FAILED,
                               "qmckl_ao_basis_primitive_vgl",
                               NULL);
      }
      ctx->ao_basis.primitive_vgl = primitive_vgl;
    }

    qmckl_exit_code rc; 
    if (ctx->ao_basis.type == 'G') {
      rc = qmckl_compute_ao_basis_primitive_gaussian_vgl(context,
                                                         ctx->ao_basis.prim_num,
                                                         ctx->electron.num,
                                                         ctx->nucleus.num,
                                                         ctx->electron.walk_num,
                                                         ctx->ao_basis.nucleus_prim_index,
                                                         ctx->electron.coord_new,
                                                         ctx->nucleus.coord,
                                                         ctx->ao_basis.exponent,
                                                         ctx->ao_basis.primitive_vgl);
    } else {
      return qmckl_failwith( context,
                             QMCKL_FAILURE,
                             "compute_ao_basis_primitive_vgl",
                             "Not yet implemented");
    } 
    if (rc != QMCKL_SUCCESS) {
      return rc;
    }

    ctx->ao_basis.primitive_vgl_date = ctx->date;
  }

  return QMCKL_SUCCESS;
}
    #+end_src

*** Compute
   :PROPERTIES:
   :Name:     qmckl_compute_ao_basis_primitive_gaussian_vgl
   :CRetType: qmckl_exit_code
   :FRetType: qmckl_exit_code
   :END:

    #+NAME: qmckl_ao_basis_primitive_gaussian_vgl_args
   | qmckl_context | context                                        | in  | Global state                                     |
   | int64_t       | prim_num                                       | in  | Number of primitives                             |
   | int64_t       | elec_num                                       | in  | Number of electrons                              |
   | int64_t       | nucl_num                                       | in  | Number of nuclei                                 |
   | int64_t       | walk_num                                       | in  | Number of walkers                                |
   | int64_t       | nucleus_prim_index[nucl_num]                   | in  | Index of the 1st primitive of each nucleus       |
   | double        | elec_coord[walk_num][3][elec_num]              | in  | Electron coordinates                             |
   | double        | nucl_coord[3][elec_num]                        | in  | Nuclear coordinates                              |
   | double        | expo[prim_num]                                 | in  | Exponents of the primitives                      |
   | double        | primitive_vgl[prim_num][5][walk_num][elec_num] | out | Value, gradients and Laplacian of the primitives |
    
    #+begin_src f90 :comments org :tangle (eval f) :noweb yes
integer function qmckl_compute_ao_basis_primitive_gaussian_vgl_f(context, &
     prim_num, elec_num, nucl_num, walk_num, &
     nucleus_prim_index, elec_coord, nucl_coord, expo, primitive_vgl) &
     result(info)
  use qmckl
  implicit none
  integer(qmckl_context), intent(in)  :: context
  integer*8             , intent(in)  :: prim_num
  integer*8             , intent(in)  :: nucl_num
  integer*8             , intent(in)  :: elec_num
  integer*8             , intent(in)  :: walk_num
  integer*8             , intent(in)  :: nucleus_prim_index(nucl_num+1)
  double precision      , intent(in)  :: elec_coord(elec_num,3,walk_num)
  double precision      , intent(in)  :: nucl_coord(nucl_num,3)
  double precision      , intent(in)  :: expo(prim_num)
  double precision      , intent(out) :: primitive_vgl(elec_num,walk_num,5,prim_num)

  integer*8 :: inucl, iprim, iwalk, ielec
  double precision :: x, y, z, two_a, ar2, r2, v, cutoff

  info = QMCKL_SUCCESS

  ! Don't compute exponentials when the result will be almost zero.
  cutoff = -dlog(1.d-15)

  do inucl=1,nucl_num
     ! C is zero-based, so shift bounds by one
     do iprim = nucleus_prim_index(inucl)+1, nucleus_prim_index(inucl+1)
        do iwalk = 1, walk_num
           do ielec = 1, elec_num
              x = elec_coord(ielec,1,iwalk) - nucl_coord(inucl,1) 
              y = elec_coord(ielec,2,iwalk) - nucl_coord(inucl,2) 
              z = elec_coord(ielec,3,iwalk) - nucl_coord(inucl,3) 

              r2 = x*x + y*y + z*z
              ar2 = expo(iprim)*r2
              if (ar2 > cutoff) cycle
              
              v = dexp(-ar2)
              two_a = -2.d0 * expo(iprim) * v

              primitive_vgl(ielec, iwalk, 1, iprim) = v
              primitive_vgl(ielec, iwalk, 2, iprim) = two_a * x 
              primitive_vgl(ielec, iwalk, 3, iprim) = two_a * y
              primitive_vgl(ielec, iwalk, 4, iprim) = two_a * z
              primitive_vgl(ielec, iwalk, 5, iprim) = two_a * (3.d0 - 2.d0*ar2)

           end do
        end do
     end do
  end do
  
end function qmckl_compute_ao_basis_primitive_gaussian_vgl_f
    #+end_src

    #+begin_src c :tangle (eval h_private_func) :comments org :exports none
qmckl_exit_code qmckl_compute_ao_basis_primitive_gaussian_vgl(
          const qmckl_context context,
          const int64_t  prim_num,
          const int64_t  elec_num,
          const int64_t  nucl_num,
          const int64_t  walk_num,
          const int64_t* nucleus_prim_index,
          const double*  elec_coord,
          const double*  nucl_coord,
          const double*  expo,
          double* const primitive_vgl);
    #+end_src

    #+CALL: generate_c_interface(table=qmckl_ao_basis_primitive_gaussian_vgl_args,rettyp=get_value("CRetType"),fname="qmckl_compute_ao_basis_primitive_gaussian_vgl"))

    #+RESULTS:
    #+begin_src f90 :tangle (eval f) :comments org :exports none
    integer(c_int32_t) function qmckl_compute_ao_basis_primitive_gaussian_vgl &
        (context, prim_num, elec_num, nucl_num, walk_num, nucleus_prim_index, elec_coord, nucl_coord, expo, primitive_vgl) &
        bind(C) result(info)

      use, intrinsic :: iso_c_binding
      implicit none

      integer (c_int64_t) , intent(in)  , value :: context
      integer (c_int64_t) , intent(in)  , value :: prim_num
      integer (c_int64_t) , intent(in)  , value :: elec_num
      integer (c_int64_t) , intent(in)  , value :: nucl_num
      integer (c_int64_t) , intent(in)  , value :: walk_num
      integer (c_int64_t) , intent(in)          :: nucleus_prim_index(nucl_num)
      real    (c_double ) , intent(in)          :: elec_coord(elec_num,3,walk_num)
      real    (c_double ) , intent(in)          :: nucl_coord(elec_num,3)
      real    (c_double ) , intent(in)          :: expo(prim_num)
      real    (c_double ) , intent(out)         :: primitive_vgl(elec_num,walk_num,5,prim_num)

      integer(c_int32_t), external :: qmckl_compute_ao_basis_primitive_gaussian_vgl_f
      info = qmckl_compute_ao_basis_primitive_gaussian_vgl_f &
             (context, prim_num, elec_num, nucl_num, walk_num, nucleus_prim_index, elec_coord, nucl_coord, expo, primitive_vgl)

    end function qmckl_compute_ao_basis_primitive_gaussian_vgl
    #+end_src

    #+begin_src python :results output :exports none
import numpy as np

def f(a,x,y):
    return np.exp( -a*(np.linalg.norm(x-y))**2 ) 

def df(a,x,y,n):
    h0 = 1.e-6
    if   n == 1: h = np.array([h0,0.,0.])
    elif n == 2: h = np.array([0.,h0,0.])
    elif n == 3: h = np.array([0.,0.,h0])
    return ( f(a,x+h,y) - f(a,x-h,y) ) / (2.*h0)

def d2f(a,x,y,n):
    h0 = 1.e-6
    if   n == 1: h = np.array([h0,0.,0.])
    elif n == 2: h = np.array([0.,h0,0.])
    elif n == 3: h = np.array([0.,0.,h0])
    return ( f(a,x+h,y) - 2.*f(a,x,y) + f(a,x-h,y) ) / h0**2

def lf(a,x,y):
    return d2f(a,x,y,1) + d2f(a,x,y,2) + d2f(a,x,y,3)

elec_26_w1 = np.array( [  1.49050402641, 2.90106987953, -1.05920815468  ] )
elec_15_w2 = np.array( [  -2.20180344582,-1.9113150239,  2.2193744778600002 ] )
nucl_1    = np.array( [ 1.096243353458458e+00, 8.907054016973815e-01, 7.777092280258892e-01 ] )
nucl_2    = np.array( [ 1.168459237342663e+00, 1.125660720053393e+00, 2.833370314829343e+00 ] )

#double prim_vgl[prim_num][5][walk_num][elec_num];
a =  0.9059; x = elec_26_w1 ; y = nucl_1
print ( "[7][0][0][26] : %e"% f(a,x,y))
print ( "[7][1][0][26] : %e"% df(a,x,y,1))
print ( "[7][2][0][26] : %e"% df(a,x,y,2))
print ( "[7][3][0][26] : %e"% df(a,x,y,3))
print ( "[7][4][0][26] : %e"% lf(a,x,y))

a =  0.32578; x = elec_15_w2 ; y = nucl_2
print ( "[39][0][1][15] : %e"% f(a,x,y))
print ( "[39][1][1][15] : %e"% df(a,x,y,1))
print ( "[39][2][1][15] : %e"% df(a,x,y,2))
print ( "[39][3][1][15] : %e"% df(a,x,y,3))
print ( "[39][4][1][15] : %e"% lf(a,x,y))

    #+end_src

    #+RESULTS:
    #+begin_example
    [7][0][0][26] : 1.050157e-03
    [7][1][0][26] : -7.501497e-04
    [7][2][0][26] : -3.825069e-03
    [7][3][0][26] : 3.495056e-03
    [7][4][0][26] : 2.040013e-02
    [39][0][1][15] : 1.083038e-03
    [39][1][1][15] : 2.378275e-03
    [39][2][1][15] : 2.143086e-03
    [39][3][1][15] : 4.332750e-04
    [39][4][1][15] : 7.514605e-03
    #+end_example

*** Test

     #+begin_src c :tangle (eval c_test) :exports none
{
#define walk_num chbrclf_walk_num
#define elec_num chbrclf_elec_num
#define prim_num chbrclf_prim_num

int64_t elec_up_num   = chbrclf_elec_up_num;
int64_t elec_dn_num   = chbrclf_elec_dn_num;
double* elec_coord    = &(chbrclf_elec_coord[0][0][0]);

rc = qmckl_set_electron_num (context, elec_up_num, elec_dn_num);  
assert (rc == QMCKL_SUCCESS);

rc = qmckl_set_electron_walk_num (context, walk_num);
assert (rc == QMCKL_SUCCESS);

assert(qmckl_electron_provided(context));

rc = qmckl_set_electron_coord (context, 'N', elec_coord);                                     
assert(rc == QMCKL_SUCCESS);



double prim_vgl[prim_num][5][walk_num][elec_num];

rc = qmckl_get_ao_basis_primitive_vgl(context, &(prim_vgl[0][0][0][0]));
assert (rc == QMCKL_SUCCESS);

assert( fabs(prim_vgl[7][0][0][26] - ( 1.0501570432064878E-003)) < 1.e-14 );
assert( fabs(prim_vgl[7][1][0][26] - (-7.5014974095310560E-004)) < 1.e-14 );
assert( fabs(prim_vgl[7][2][0][26] - (-3.8250692897610380E-003)) < 1.e-14 );
assert( fabs(prim_vgl[7][3][0][26] - ( 3.4950559194080275E-003)) < 1.e-14 );
assert( fabs(prim_vgl[7][4][0][26] - ( 2.0392163767356572E-002)) < 1.e-14 );
  
assert( fabs(prim_vgl[39][0][1][15] - ( 1.0825844173157661E-003)) < 1.e-14 );
assert( fabs(prim_vgl[39][1][1][15] - ( 2.3774237611651531E-003)) < 1.e-14 );
assert( fabs(prim_vgl[39][2][1][15] - ( 2.1423191526963063E-003)) < 1.e-14 );
assert( fabs(prim_vgl[39][3][1][15] - ( 4.3312003523048492E-004)) < 1.e-14 );
assert( fabs(prim_vgl[39][4][1][15] - ( 7.5174404780004771E-003)) < 1.e-14 );
  
}


     #+end_src

*** Ideas for improvement

    #+begin_src c
// m : walkers
// j : electrons
// l : primitives

k=0;
for (m=0 ; m<walk_num ; ++m) {
  for (j=0 ; j<elec_num ; ++j) {
    for (i=0 ; i<nucl_num ; ++i) {
      
      r2 = nucl_elec_dist[i][j];
      
      if (r2 < nucl_radius2[i]) {
        
        for (l=0 ; l<prim_num ; ++l) {
          tmp[k].i   = i;
          tmp[k].j   = j;
          tmp[k].m   = m;
          tmp[k].ar2 = -expo[l] *r2;
          ++k;
        }
      }
    }
  }
 }

// sort(tmp) in increasing ar2;
// Identify first ar2 above numerical accuracy threshold
// Compute vectorized exponentials on significant values
    #+end_src

** Computation of shells

*** Get

    #+begin_src c :comments org :tangle (eval h_func) :noweb yes
qmckl_exit_code qmckl_get_ao_basis_shell_vgl(qmckl_context context, double* const shell_vgl);
    #+end_src

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_get_ao_basis_shell_vgl(qmckl_context context, double* const shell_vgl) {
  
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return QMCKL_NULL_CONTEXT;
  }

  qmckl_exit_code rc;

  rc = qmckl_provide_ao_basis_shell_vgl(context);
  if (rc != QMCKL_SUCCESS) return rc;

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  size_t sze = ctx->ao_basis.shell_num * 5 * ctx->electron.num * ctx->electron.walk_num;
  memcpy(shell_vgl, ctx->ao_basis.shell_vgl, sze * sizeof(double));

  return QMCKL_SUCCESS;
}
    #+end_src

*** Provide

    #+begin_src c :comments org :tangle (eval h_private_func) :noweb yes :exports none
qmckl_exit_code qmckl_provide_ao_basis_shell_vgl(qmckl_context context);
    #+end_src

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_provide_ao_basis_shell_vgl(qmckl_context context)
{

  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return QMCKL_NULL_CONTEXT;
  }

  qmckl_context_struct* const ctx = (qmckl_context_struct* const) context;
  assert (ctx != NULL);

  if (!ctx->ao_basis.provided) {
    return qmckl_failwith( context,
                           QMCKL_NOT_PROVIDED,
                           "qmckl_ao_basis_shell_vgl",
                           NULL);
  }
  
 /* Compute if necessary */
  if (ctx->electron.coord_new_date > ctx->ao_basis.shell_vgl_date) {

 /* Allocate array */
    if (ctx->ao_basis.shell_vgl == NULL) {

      qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
      mem_info.size = ctx->ao_basis.prim_num * 5 * ctx->electron.num *
        ctx->electron.walk_num * sizeof(double);
      double* shell_vgl = (double*) qmckl_malloc(context, mem_info);

      if (shell_vgl == NULL) {
        return qmckl_failwith( context,
                               QMCKL_ALLOCATION_FAILED,
                               "qmckl_ao_basis_shell_vgl",
                               NULL);
      }
      ctx->ao_basis.shell_vgl = shell_vgl;
    }

    qmckl_exit_code rc; 
    if (ctx->ao_basis.type == 'G') {
      rc = qmckl_compute_ao_basis_shell_gaussian_vgl(context,
                                                         ctx->ao_basis.prim_num,
                                                         ctx->ao_basis.shell_num,
                                                         ctx->electron.num,
                                                         ctx->nucleus.num,
                                                         ctx->electron.walk_num,
                                                         ctx->ao_basis.nucleus_shell_num,
                                                         ctx->ao_basis.nucleus_index,
                                                         ctx->ao_basis.shell_prim_index,
                                                         ctx->ao_basis.shell_prim_num,
                                                         ctx->electron.coord_new,
                                                         ctx->nucleus.coord,
                                                         ctx->ao_basis.exponent,
                                                         ctx->ao_basis.coefficient,
                                                         ctx->ao_basis.shell_vgl);
    } else {
      return qmckl_failwith( context,
                             QMCKL_FAILURE,
                             "compute_ao_basis_shell_vgl",
                             "Not yet implemented");
    } 
    if (rc != QMCKL_SUCCESS) {
      return rc;
    }

    ctx->ao_basis.shell_vgl_date = ctx->date;
  }

  return QMCKL_SUCCESS;
}
    #+end_src

*** Compute
   :PROPERTIES:
   :Name:     qmckl_compute_ao_basis_shell_gaussian_vgl
   :CRetType: qmckl_exit_code
   :FRetType: qmckl_exit_code
   :END:

    #+NAME: qmckl_ao_basis_shell_gaussian_vgl_args
   | ~qmckl_context~ | ~context~                                     | in  | Global state                                 |
   | ~int64_t~       | ~prim_num~                                    | in  | Number of primitives                         |
   | ~int64_t~       | ~shell_num~                                   | in  | Number of shells                             |
   | ~int64_t~       | ~elec_num~                                    | in  | Number of electrons                          |
   | ~int64_t~       | ~nucl_num~                                    | in  | Number of nuclei                             |
   | ~int64_t~       | ~walk_num~                                    | in  | Number of walkers                            |
   | ~int64_t~       | ~nucleus_shell_num[nucl_num]~                 | in  | Number of shells for each nucleus            |
   | ~int64_t~       | ~nucleus_index[nucl_num]~                     | in  | Index of the 1st shell of each nucleus       |
   | ~int64_t~       | ~shell_prim_index[shell_num]~                 | in  | Index of the 1st primitive of each shell     |
   | ~int64_t~       | ~shell_prim_num[shell_num]~                   | in  | Number of primitives per shell               |
   | ~double~        | ~elec_coord[walk_num][3][elec_num]~           | in  | Electron coordinates                         |
   | ~double~        | ~nucl_coord[3][elec_num]~                     | in  | Nuclear coordinates                          |
   | ~double~        | ~expo[prim_num]~                              | in  | Exponents of the primitives                  |
   | ~double~        | ~coef[prim_num]~                              | in  | Coefficients of the primitives               |
   | ~double~        | ~shell_vgl[shell_num][5][walk_num][elec_num]~ | out | Value, gradients and Laplacian of the shells |
    
    #+begin_src f90 :comments org :tangle (eval f) :noweb yes
integer function qmckl_compute_ao_basis_shell_gaussian_vgl_f(context, &
     prim_num, shell_num, elec_num, nucl_num, walk_num, &
     nucleus_shell_num, nucleus_index, shell_prim_index, shell_prim_num, &
     elec_coord, nucl_coord, expo, coef, shell_vgl) &
     result(info)
  use qmckl
  implicit none
  integer(qmckl_context), intent(in)  :: context
  integer*8             , intent(in)  :: prim_num
  integer*8             , intent(in)  :: shell_num
  integer*8             , intent(in)  :: nucl_num
  integer*8             , intent(in)  :: elec_num
  integer*8             , intent(in)  :: walk_num
  integer*8             , intent(in)  :: nucleus_shell_num(nucl_num)
  integer*8             , intent(in)  :: nucleus_index(nucl_num)
  integer*8             , intent(in)  :: shell_prim_index(shell_num)
  integer*8             , intent(in)  :: shell_prim_num(shell_num)
  double precision      , intent(in)  :: elec_coord(elec_num,3,walk_num)
  double precision      , intent(in)  :: nucl_coord(nucl_num,3)
  double precision      , intent(in)  :: expo(prim_num)
  double precision      , intent(in)  :: coef(prim_num)
  double precision      , intent(out) :: shell_vgl(elec_num,walk_num,5,shell_num)

  integer*8 :: inucl, iprim, iwalk, ielec, ishell
  double precision :: x, y, z, two_a, ar2, r2, v, cutoff

  info = QMCKL_SUCCESS
  
  ! Don't compute exponentials when the result will be almost zero.
  cutoff = -dlog(1.d-15)

  do inucl=1,nucl_num
     do ishell=nucleus_index(inucl)+1, nucleus_index(inucl)+nucleus_shell_num(inucl)
        ! C is zero-based, so shift bounds by one

        do iwalk = 1, walk_num
           do ielec = 1, elec_num

              shell_vgl(ielec, iwalk, 1:5, ishell) = 0.d0

              x = elec_coord(ielec,1,iwalk) - nucl_coord(inucl,1) 
              y = elec_coord(ielec,2,iwalk) - nucl_coord(inucl,2) 
              z = elec_coord(ielec,3,iwalk) - nucl_coord(inucl,3) 

              r2 = x*x + y*y + z*z

              do iprim = shell_prim_index(ishell)+1, shell_prim_index(ishell)+shell_prim_num(ishell)

                 ar2 = expo(iprim)*r2
                 if (ar2 > cutoff) then
                    cycle
                 end if

                 v = coef(iprim) * dexp(-ar2)
                 two_a = -2.d0 * expo(iprim) * v
                 
                 shell_vgl(ielec, iwalk, 1, ishell) = &
                      shell_vgl(ielec, iwalk, 1, ishell) + v
                 
                 shell_vgl(ielec, iwalk, 2, ishell) = &
                      shell_vgl(ielec, iwalk, 2, ishell) + two_a * x 
                 
                 shell_vgl(ielec, iwalk, 3, ishell) = &
                      shell_vgl(ielec, iwalk, 3, ishell) + two_a * y 
                 
                 shell_vgl(ielec, iwalk, 4, ishell) = &
                      shell_vgl(ielec, iwalk, 4, ishell) + two_a * z 
                 
                 shell_vgl(ielec, iwalk, 5, ishell) = &
                      shell_vgl(ielec, iwalk, 5, ishell) + two_a * (3.d0 - 2.d0*ar2)

              end do
              
           end do
        end do
        
     end do
  end do
  
end function qmckl_compute_ao_basis_shell_gaussian_vgl_f
    #+end_src


    #+begin_src c :tangle (eval h_private_func) :comments org :exports none
qmckl_exit_code qmckl_compute_ao_basis_shell_gaussian_vgl(
          const qmckl_context context,
          const int64_t  prim_num,
          const int64_t  shell_num,
          const int64_t  elec_num,
          const int64_t  nucl_num,
          const int64_t  walk_num,
          const int64_t* nucleus_shell_num,
          const int64_t* shell_prim_index,
          const int64_t* nucleus_index,
          const int64_t* shell_prim_num,
          const double*  elec_coord,
          const double*  nucl_coord,
          const double*  expo,
          const double*  coef,
          double* const shell_vgl);
    #+end_src

    #+CALL: generate_c_interface(table=qmckl_ao_basis_shell_gaussian_vgl_args,rettyp=get_value("CRetType"),fname="qmckl_compute_ao_basis_shell_gaussian_vgl"))

    #+RESULTS:
    #+begin_src f90 :tangle (eval f) :comments org :exports none
    integer(c_int32_t) function qmckl_compute_ao_basis_shell_gaussian_vgl &
        (context, &
         prim_num, &
         shell_num, &
         elec_num, &
         nucl_num, &
         walk_num, &
         nucleus_shell_num, &
         nucleus_index, &
         shell_prim_index, &
         shell_prim_num, &
         elec_coord, &
         nucl_coord, &
         expo, &
         coef, &
         shell_vgl) &
        bind(C) result(info)

      use, intrinsic :: iso_c_binding
      implicit none

      integer (c_int64_t) , intent(in)  , value :: context
      integer (c_int64_t) , intent(in)  , value :: prim_num
      integer (c_int64_t) , intent(in)  , value :: shell_num
      integer (c_int64_t) , intent(in)  , value :: elec_num
      integer (c_int64_t) , intent(in)  , value :: nucl_num
      integer (c_int64_t) , intent(in)  , value :: walk_num
      integer (c_int64_t) , intent(in)          :: nucleus_shell_num(nucl_num)
      integer (c_int64_t) , intent(in)          :: nucleus_index(nucl_num)
      integer (c_int64_t) , intent(in)          :: shell_prim_index(shell_num)
      integer (c_int64_t) , intent(in)          :: shell_prim_num(shell_num)
      real    (c_double ) , intent(in)          :: elec_coord(elec_num,3,walk_num)
      real    (c_double ) , intent(in)          :: nucl_coord(elec_num,3)
      real    (c_double ) , intent(in)          :: expo(prim_num)
      real    (c_double ) , intent(in)          :: coef(prim_num)
      real    (c_double ) , intent(out)         :: shell_vgl(elec_num,walk_num,5,shell_num)

      integer(c_int32_t), external :: qmckl_compute_ao_basis_shell_gaussian_vgl_f
      info = qmckl_compute_ao_basis_shell_gaussian_vgl_f &
             (context, &
         prim_num, &
         shell_num, &
         elec_num, &
         nucl_num, &
         walk_num, &
         nucleus_shell_num, &
         nucleus_index, &
         shell_prim_index, &
         shell_prim_num, &
         elec_coord, &
         nucl_coord, &
         expo, &
         coef, &
         shell_vgl)

    end function qmckl_compute_ao_basis_shell_gaussian_vgl
    #+end_src

    #+begin_src python :results output :exports none
import numpy as np

def f(a,x,y):
    return np.sum( [c * np.exp( -b*(np.linalg.norm(x-y))**2) for b,c in a] ) 

def df(a,x,y,n):
    h0 = 1.e-6
    if   n == 1: h = np.array([h0,0.,0.])
    elif n == 2: h = np.array([0.,h0,0.])
    elif n == 3: h = np.array([0.,0.,h0])
    return ( f(a,x+h,y) - f(a,x-h,y) ) / (2.*h0)

def d2f(a,x,y,n):
    h0 = 1.e-6
    if   n == 1: h = np.array([h0,0.,0.])
    elif n == 2: h = np.array([0.,h0,0.])
    elif n == 3: h = np.array([0.,0.,h0])
    return ( f(a,x+h,y) - 2.*f(a,x,y) + f(a,x-h,y) ) / h0**2

def lf(a,x,y):
    return d2f(a,x,y,1) + d2f(a,x,y,2) + d2f(a,x,y,3)

elec_26_w1 = np.array( [  1.49050402641, 2.90106987953, -1.05920815468  ] )
elec_15_w2 = np.array( [  -2.20180344582,-1.9113150239,  2.2193744778600002 ] )
nucl_1    = np.array( [ 1.096243353458458e+00, 8.907054016973815e-01, 7.777092280258892e-01 ] )
nucl_2    = np.array( [ 1.168459237342663e+00, 1.125660720053393e+00, 2.833370314829343e+00 ] )

#double prim_vgl[prim_num][5][walk_num][elec_num];
x = elec_26_w1 ; y = nucl_1
a = [(  8.236000E+03,  -1.130000E-04  ),
     (  1.235000E+03,  -8.780000E-04  ),
     (  2.808000E+02,  -4.540000E-03  ),
     (  7.927000E+01,  -1.813300E-02  ),
     (  2.559000E+01,  -5.576000E-02  ),
     (  8.997000E+00,  -1.268950E-01  ),
     (  3.319000E+00,  -1.703520E-01  ),
     (  9.059000E-01,   1.403820E-01  ),
     (  3.643000E-01,   5.986840E-01  ),
     (  1.285000E-01,   3.953890E-01  )]

print ( "[1][0][0][26] : %e"% f(a,x,y))
print ( "[1][1][0][26] : %e"% df(a,x,y,1))
print ( "[1][2][0][26] : %e"% df(a,x,y,2))
print ( "[1][3][0][26] : %e"% df(a,x,y,3))
print ( "[1][4][0][26] : %e"% lf(a,x,y))

x = elec_15_w2 ; y = nucl_2
a = [(3.387000E+01, 6.068000E-03),
     (5.095000E+00, 4.530800E-02),
     (1.159000E+00, 2.028220E-01),
     (3.258000E-01, 5.039030E-01),
     (1.027000E-01, 3.834210E-01)]

print ( "[14][0][1][15] : %e"% f(a,x,y))
print ( "[14][1][1][15] : %e"% df(a,x,y,1))
print ( "[14][2][1][15] : %e"% df(a,x,y,2))
print ( "[14][3][1][15] : %e"% df(a,x,y,3))
print ( "[14][4][1][15] : %e"% lf(a,x,y))

    #+end_src

    #+RESULTS:
    #+begin_example
    [1][0][0][26] : 1.875569e-01
    [1][1][0][26] : -2.615250e-02
    [1][2][0][26] : -1.333535e-01
    [1][3][0][26] : 1.218483e-01
    [1][4][0][26] : 3.227973e-02
    [14][0][1][15] : 4.509748e-02
    [14][1][1][15] : 3.203918e-02
    [14][2][1][15] : 2.887081e-02
    [14][3][1][15] : 5.836910e-03
    [14][4][1][15] : 1.564721e-02
    #+end_example

*** Test

     #+begin_src c :tangle (eval c_test) :exports none
{
#define walk_num chbrclf_walk_num
#define elec_num chbrclf_elec_num
#define shell_num chbrclf_shell_num

int64_t elec_up_num   = chbrclf_elec_up_num;
int64_t elec_dn_num   = chbrclf_elec_dn_num;
double* elec_coord    = &(chbrclf_elec_coord[0][0][0]);

rc = qmckl_set_electron_num (context, elec_up_num, elec_dn_num);  
assert (rc == QMCKL_SUCCESS);

rc = qmckl_set_electron_walk_num (context, walk_num);
assert (rc == QMCKL_SUCCESS);

assert(qmckl_electron_provided(context));

rc = qmckl_set_electron_coord (context, 'N', elec_coord);                                     
assert(rc == QMCKL_SUCCESS);


double shell_vgl[shell_num][5][walk_num][elec_num];

rc = qmckl_get_ao_basis_shell_vgl(context, &(shell_vgl[0][0][0][0]));
assert (rc == QMCKL_SUCCESS);

printf(" shell_vgl[1][0][0][26] %25.15e\n", shell_vgl[1][0][0][26]);
printf(" shell_vgl[1][1][0][26] %25.15e\n", shell_vgl[1][1][0][26]);
printf(" shell_vgl[1][2][0][26] %25.15e\n", shell_vgl[1][2][0][26]);
printf(" shell_vgl[1][3][0][26] %25.15e\n", shell_vgl[1][3][0][26]);
printf(" shell_vgl[1][4][0][26] %25.15e\n", shell_vgl[1][4][0][26]);
  
printf(" shell_vgl[14][0][1][15] %25.15e\n", shell_vgl[14][0][1][15]);
printf(" shell_vgl[14][1][1][15] %25.15e\n", shell_vgl[14][1][1][15]);
printf(" shell_vgl[14][2][1][15] %25.15e\n", shell_vgl[14][2][1][15]);
printf(" shell_vgl[14][3][1][15] %25.15e\n", shell_vgl[14][3][1][15]);
printf(" shell_vgl[14][4][1][15] %25.15e\n", shell_vgl[14][4][1][15]);

assert( fabs(shell_vgl[1][0][0][26] - (  1.875568658202993e-01)) < 1.e-14 );
assert( fabs(shell_vgl[1][1][0][26] - ( -2.615250164814435e-02)) < 1.e-14 );
assert( fabs(shell_vgl[1][2][0][26] - ( -1.333535498894419e-01)) < 1.e-14 );
assert( fabs(shell_vgl[1][3][0][26] - (  1.218482800201208e-01)) < 1.e-14 );
assert( fabs(shell_vgl[1][4][0][26] - (  3.197054084474042e-02)) < 1.e-14 );
  
assert( fabs(shell_vgl[14][0][1][15] - ( 4.509748459243634e-02)) < 1.e-14 );
assert( fabs(shell_vgl[14][1][1][15] - ( 3.203917730584210e-02)) < 1.e-14 );
assert( fabs(shell_vgl[14][2][1][15] - ( 2.887080725789477e-02)) < 1.e-14 );
assert( fabs(shell_vgl[14][3][1][15] - ( 5.836910453297223e-03)) < 1.e-14 );
assert( fabs(shell_vgl[14][4][1][15] - ( 1.572966698871693e-02)) < 1.e-14 );
}  
     #+end_src


* Polynomial part
** General functions for Powers of $x-X_i$
   :PROPERTIES:
   :Name:     qmckl_ao_power
   :CRetType: qmckl_exit_code
   :FRetType: qmckl_exit_code
   :END:

   The ~qmckl_ao_power~ function computes all the powers of the ~n~
   input data up to the given maximum value given in input for each of
   the $n$ points:

   \[ P_{ik} = X_i^k \]

   #+NAME: qmckl_ao_power_args
   | qmckl_context | context   | in  | Global state                                      |
   | int64_t       | n         | in  | Number of values                                  |
   | double        | X[n]      | in  | Array containing the input values                 |
   | int32_t       | LMAX[n]   | in  | Array containing the maximum power for each value |
   | double        | P[n][ldp] | out | Array containing all the powers of ~X~            |
   | int64_t       | ldp       | in  | Leading dimension of array ~P~                    |

*** Requirements

    - ~context~ is not ~QMCKL_NULL_CONTEXT~
    - ~n~ > 0
    - ~X~ is allocated with at least $n \times 8$ bytes
    - ~LMAX~ is allocated with at least $n \times 4$ bytes
    - ~P~ is allocated with at least $n \times \max_i \text{LMAX}_i \times 8$ bytes
    - ~LDP~ >= $\max_i$ ~LMAX[i]~

*** C Header

    #+CALL: generate_c_header(table=qmckl_ao_power_args,rettyp=get_value("CRetType"),fname="qmckl_ao_power")

    #+RESULTS:
    #+begin_src c :tangle (eval h_func) :comments org
    qmckl_exit_code qmckl_ao_power (
          const qmckl_context context,
          const int64_t n,
          const double* X,
          const int32_t* LMAX,
          double* const P,
          const int64_t ldp ); 
    #+end_src

*** Source

    #+begin_src f90 :tangle (eval f)
integer function qmckl_ao_power_f(context, n, X, LMAX, P, ldp) result(info)
  use qmckl
  implicit none
  integer*8 , intent(in)  :: context
  integer*8 , intent(in)  :: n
  real*8    , intent(in)  :: X(n)
  integer   , intent(in)  :: LMAX(n)
  real*8    , intent(out) :: P(ldp,n)
  integer*8 , intent(in)  :: ldp

  integer*8  :: i,k

  info = QMCKL_SUCCESS

  if (context == QMCKL_NULL_CONTEXT) then
     info = QMCKL_INVALID_CONTEXT
     return
  endif

  if (n <= ldp) then
     info = QMCKL_INVALID_ARG_2
     return
  endif

  k = MAXVAL(LMAX)
  if (LDP < k) then
     info = QMCKL_INVALID_ARG_6
     return
  endif

  if (k <= 0) then
     info = QMCKL_INVALID_ARG_4
     return
  endif

  do i=1,n
     P(1,i) = X(i)
     do k=2,LMAX(i)
        P(k,i) = P(k-1,i) * X(i)
     end do
  end do

end function qmckl_ao_power_f
    #+end_src

*** C interface
    #+CALL: generate_c_interface(table=qmckl_ao_power_args,rettyp=get_value("CRetType"),fname="qmckl_ao_power")

    #+RESULTS:
    #+begin_src f90 :tangle (eval f) :comments org :exports none
    integer(c_int32_t) function qmckl_ao_power &
        (context, n, X, LMAX, P, ldp) &
        bind(C) result(info)

      use, intrinsic :: iso_c_binding
      implicit none

      integer (c_int64_t) , intent(in)  , value :: context
      integer (c_int64_t) , intent(in)  , value :: n
      real    (c_double ) , intent(in)          :: X(n)
      integer (c_int32_t) , intent(in)          :: LMAX(n)
      real    (c_double ) , intent(out)         :: P(ldp,n)
      integer (c_int64_t) , intent(in)  , value :: ldp

      integer(c_int32_t), external :: qmckl_ao_power_f
      info = qmckl_ao_power_f &
             (context, n, X, LMAX, P, ldp)

    end function qmckl_ao_power
    #+end_src

*** Fortran interface

    #+CALL: generate_f_interface(table=qmckl_ao_power_args,rettyp=get_value("CRetType"),fname="qmckl_ao_power")

    #+RESULTS:
    #+begin_src f90 :tangle (eval fh_func) :comments org :exports none
    interface
      integer(c_int32_t) function qmckl_ao_power &
          (context, n, X, LMAX, P, ldp) &
          bind(C)
        use, intrinsic :: iso_c_binding
        import
        implicit none

        integer (c_int64_t) , intent(in)  , value :: context
        integer (c_int64_t) , intent(in)  , value :: n
        real    (c_double ) , intent(in)          :: X(n)
        integer (c_int32_t) , intent(in)          :: LMAX(n)
        real    (c_double ) , intent(out)         :: P(ldp,n)
        integer (c_int64_t) , intent(in)  , value :: ldp

      end function qmckl_ao_power
    end interface
    #+end_src

*** Test

    #+begin_src f90 :tangle (eval f_test)
integer(c_int32_t) function test_qmckl_ao_power(context) bind(C)
  use qmckl
  implicit none

  integer(qmckl_context), intent(in), value :: context

  integer*8                     :: n, LDP
  integer, allocatable          :: LMAX(:)
  double precision, allocatable :: X(:), P(:,:)
  integer*8                     :: i,j
  double precision              :: epsilon

  epsilon = qmckl_get_numprec_epsilon(context)

  n = 100;
  LDP = 10;

  allocate(X(n), P(LDP,n), LMAX(n))

  do j=1,n
     X(j) = -5.d0 + 0.1d0 * dble(j)
     LMAX(j) = 1 + int(mod(j, 5),4)
  end do

  test_qmckl_ao_power = qmckl_ao_power(context, n, X, LMAX, P, LDP)
  if (test_qmckl_ao_power /= QMCKL_SUCCESS) return

  test_qmckl_ao_power = QMCKL_FAILURE

  do j=1,n
     do i=1,LMAX(j)
        if ( X(j)**i == 0.d0 ) then
           if ( P(i,j) /= 0.d0) return
        else
           if ( dabs(1.d0 - P(i,j) / (X(j)**i)) > epsilon ) return
        end if
     end do
  end do

  test_qmckl_ao_power = QMCKL_SUCCESS
  deallocate(X,P,LMAX)
end function test_qmckl_ao_power
    #+end_src

    #+begin_src c :tangle (eval c_test) :exports none
    int  test_qmckl_ao_power(qmckl_context context);
    assert(0 == test_qmckl_ao_power(context));
    #+end_src

** General functions for Value, Gradient and Laplacian of a polynomial
   :PROPERTIES:
   :Name:     qmckl_ao_polynomial_vgl
   :CRetType: qmckl_exit_code
   :FRetType: qmckl_exit_code
   :END:

   A polynomial is centered on a nucleus $\mathbf{R}_i$

   \[
   P_l(\mathbf{r},\mathbf{R}_i)  =   (x-X_i)^a (y-Y_i)^b (z-Z_i)^c
   \]

   The gradients with respect to electron coordinates are

   \begin{eqnarray*}
   \frac{\partial }{\partial x} P_l\left(\mathbf{r},\mathbf{R}_i \right) &
                  = & a (x-X_i)^{a-1} (y-Y_i)^b (z-Z_i)^c \\
   \frac{\partial }{\partial y} P_l\left(\mathbf{r},\mathbf{R}_i \right) &
                  = & b (x-X_i)^a (y-Y_i)^{b-1} (z-Z_i)^c \\
   \frac{\partial }{\partial z} P_l\left(\mathbf{r},\mathbf{R}_i \right) &
                  = & c (x-X_i)^a (y-Y_i)^b (z-Z_i)^{c-1} \\
   \end{eqnarray*}

   and the Laplacian is

   \begin{eqnarray*}
   \left( \frac{\partial }{\partial x^2} +
              \frac{\partial }{\partial y^2} +
              \frac{\partial }{\partial z^2} \right) P_l
              \left(\mathbf{r},\mathbf{R}_i \right) &  = &
            a(a-1) (x-X_i)^{a-2} (y-Y_i)^b (z-Z_i)^c + \\
         && b(b-1) (x-X_i)^a (y-Y_i)^{b-1} (z-Z_i)^c + \\
         && c(c-1) (x-X_i)^a (y-Y_i)^b (z-Z_i)^{c-1}.
   \end{eqnarray*}

 ~qmckl_ao_polynomial_vgl~ computes the values, gradients and
   Laplacians at a given point in space, of all polynomials with an
   angular momentum up to ~lmax~.

   #+NAME: qmckl_ao_polynomial_vgl_args
   | qmckl_context | context     | in    | Global state                                         |
   | double        | X[3]        | in    | Array containing the coordinates of the points       |
   | double        | R[3]        | in    | Array containing the x,y,z coordinates of the center |
   | int32_t       | lmax        | in    | Maximum angular momentum                             |
   | int64_t       | n           | inout | Number of computed polynomials                       |
   | int32_t       | L[n][ldl]   | out   | Contains a,b,c for all ~n~ results                   |
   | int64_t       | ldl         | in    | Leading dimension of ~L~                             |
   | double        | VGL[n][ldv] | out   | Value, gradients and Laplacian of the polynomials    |
   | int64_t       | ldv         | in    | Leading dimension of array ~VGL~                     |

*** Requirements

    - ~context~ is not ~QMCKL_NULL_CONTEXT~
    - ~n~ > 0
    - ~lmax~ >= 0
    - ~ldl~ >= 3
    - ~ldv~ >= 5
    - ~X~ is allocated with at least $3 \times 8$ bytes
    - ~R~ is allocated with at least $3 \times 8$ bytes
    - ~n~ >= ~(lmax+1)(lmax+2)(lmax+3)/6~
    - ~L~ is allocated with at least $3 \times n \times 4$ bytes
    - ~VGL~ is allocated with at least $5 \times n \times 8$ bytes
    - On output, ~n~ should be equal to ~(lmax+1)(lmax+2)(lmax+3)/6~
    - On output, the powers are given in the following order (l=a+b+c):
      - Increasing values of ~l~
      - Within a given value of ~l~, alphabetical order of the
        string made by a*"x" + b*"y" + c*"z" (in Python notation).
        For example, with a=0, b=2 and c=1 the string is "yyz"

*** C Header

    #+CALL: generate_c_header(table=qmckl_ao_polynomial_vgl_args,rettyp=get_value("CRetType"),fname=get_value("Name"))

    #+RESULTS:
    #+begin_src c :tangle (eval h_func) :comments org
    qmckl_exit_code qmckl_ao_polynomial_vgl (
          const qmckl_context context,
          const double* X,
          const double* R,
          const int32_t lmax,
          int64_t* n,
          int32_t* const L,
          const int64_t ldl,
          double* const VGL,
          const int64_t ldv );
    #+end_src

*** Source
    #+begin_src f90 :tangle (eval f)
integer function qmckl_ao_polynomial_vgl_f(context, X, R, lmax, n, L, ldl, VGL, ldv) result(info)
  use qmckl
  implicit none
  integer*8 , intent(in)  :: context
  real*8    , intent(in)  :: X(3), R(3)
  integer   , intent(in)  :: lmax
  integer*8 , intent(out) :: n
  integer   , intent(out) :: L(ldl,(lmax+1)*(lmax+2)*(lmax+3)/6)
  integer*8 , intent(in)  :: ldl
  real*8    , intent(out) :: VGL(ldv,(lmax+1)*(lmax+2)*(lmax+3)/6)
  integer*8 , intent(in)  :: ldv

  integer*8         :: i,j
  integer           :: a,b,c,d
  real*8            :: Y(3)
  integer           :: lmax_array(3)
  real*8            :: pows(-2:lmax,3)
  integer, external :: qmckl_ao_power_f
  double precision  :: xy, yz, xz
  double precision  :: da, db, dc, dd

  info = 0

  if (context == QMCKL_NULL_CONTEXT) then
     info = QMCKL_INVALID_CONTEXT
     return
  endif

  if (lmax < 0) then
     info = QMCKL_INVALID_ARG_4
     return
  endif

  if (ldl < 3) then
     info = QMCKL_INVALID_ARG_7
     return
  endif

  if (ldv < 5) then
     info = QMCKL_INVALID_ARG_9
     return
  endif


  do i=1,3
     Y(i) = X(i) - R(i)
  end do

  lmax_array(1:3) = lmax
  if (lmax == 0) then
     VGL(1,1) = 1.d0
     vgL(2:5,1) = 0.d0
     l(1:3,1) = 0
     n=1
  else if (lmax > 0) then
     pows(-2:0,1:3) = 1.d0
     do i=1,lmax
        pows(i,1) = pows(i-1,1) * Y(1)
        pows(i,2) = pows(i-1,2) * Y(2)
        pows(i,3) = pows(i-1,3) * Y(3)
     end do

     VGL(1:5,1:4) = 0.d0
     l  (1:3,1:4) = 0

     VGL(1  ,1  ) = 1.d0
     vgl(1:5,2:4) = 0.d0

     l  (1,2) = 1
     vgl(1,2) = pows(1,1)
     vgL(2,2) = 1.d0

     l  (2,3) = 1
     vgl(1,3) = pows(1,2)
     vgL(3,3) = 1.d0

     l  (3,4) = 1
     vgl(1,4) = pows(1,3)
     vgL(4,4) = 1.d0

     n=4
  endif

  ! l>=2
  dd = 2.d0
  do d=2,lmax
     da = dd
     do a=d,0,-1
        db = dd-da
        do b=d-a,0,-1
           c  = d  - a  - b
           dc = dd - da - db
           n = n+1

           l(1,n) = a
           l(2,n) = b
           l(3,n) = c

           xy = pows(a,1) * pows(b,2)
           yz = pows(b,2) * pows(c,3)
           xz = pows(a,1) * pows(c,3)

           vgl(1,n) = xy * pows(c,3)

           xy = dc * xy
           xz = db * xz
           yz = da * yz

           vgl(2,n) = pows(a-1,1) * yz
           vgl(3,n) = pows(b-1,2) * xz
           vgl(4,n) = pows(c-1,3) * xy

           vgl(5,n) = &
                (da-1.d0) * pows(a-2,1) * yz + &
                (db-1.d0) * pows(b-2,2) * xz + &
                (dc-1.d0) * pows(c-2,3) * xy

           db = db - 1.d0
        end do
        da = da - 1.d0
     end do
     dd = dd + 1.d0
  end do

  info = QMCKL_SUCCESS

end function qmckl_ao_polynomial_vgl_f
    #+end_src

*** C interface

    #+CALL: generate_c_interface(table=qmckl_ao_polynomial_vgl_args,rettyp=get_value("CRetType"),fname=get_value("Name"))

    #+RESULTS:
    #+begin_src f90 :tangle (eval f) :comments org :exports none
    integer(c_int32_t) function qmckl_ao_polynomial_vgl &
        (context, X, R, lmax, n, L, ldl, VGL, ldv) &
        bind(C) result(info)

      use, intrinsic :: iso_c_binding
      implicit none

      integer (c_int64_t) , intent(in)  , value :: context
      real    (c_double ) , intent(in)          :: X(3)
      real    (c_double ) , intent(in)          :: R(3)
      integer (c_int32_t) , intent(in)  , value :: lmax
      integer (c_int64_t) , intent(inout)        :: n
      integer (c_int32_t) , intent(out)         :: L(ldl,n)
      integer (c_int64_t) , intent(in)  , value :: ldl
      real    (c_double ) , intent(out)         :: VGL(ldv,n)
      integer (c_int64_t) , intent(in)  , value :: ldv

      integer(c_int32_t), external :: qmckl_ao_polynomial_vgl_f
      info = qmckl_ao_polynomial_vgl_f &
             (context, X, R, lmax, n, L, ldl, VGL, ldv)

    end function qmckl_ao_polynomial_vgl
    #+end_src

*** Fortran interface

    #+CALL: generate_f_interface(table=qmckl_ao_polynomial_vgl_args,rettyp=get_value("FRetType"),fname=get_value("Name"))

    #+RESULTS:
    #+begin_src f90 :tangle (eval fh_func) :comments org :exports none
    interface
      integer(c_int32_t) function qmckl_ao_polynomial_vgl &
          (context, X, R, lmax, n, L, ldl, VGL, ldv) &
          bind(C)
        use, intrinsic :: iso_c_binding
        import
        implicit none

        integer (c_int64_t) , intent(in)  , value :: context
        real    (c_double ) , intent(in)          :: X(3)
        real    (c_double ) , intent(in)          :: R(3)
        integer (c_int32_t) , intent(in)  , value :: lmax
        integer (c_int64_t) , intent(inout)        :: n
        integer (c_int32_t) , intent(out)         :: L(ldl,n)
        integer (c_int64_t) , intent(in)  , value :: ldl
        real    (c_double ) , intent(out)         :: VGL(ldv,n)
        integer (c_int64_t) , intent(in)  , value :: ldv

      end function qmckl_ao_polynomial_vgl
    end interface
    #+end_src

*** Test

    #+begin_src f90 :tangle (eval f_test)
integer(c_int32_t) function test_qmckl_ao_polynomial_vgl(context) bind(C)
  use qmckl
  implicit none

  integer(c_int64_t), intent(in), value :: context

  integer                       :: lmax, d, i
  integer, allocatable          :: L(:,:)
  integer*8                     :: n, ldl, ldv, j
  double precision              :: X(3), R(3), Y(3)
  double precision, allocatable :: VGL(:,:)
  double precision              :: w
  double precision              :: epsilon

  epsilon = qmckl_get_numprec_epsilon(context)

  X = (/ 1.1 , 2.2 ,  3.3 /)
  R = (/ 0.1 , 1.2 , -2.3 /)
  Y(:) = X(:) - R(:)

  lmax = 4;
  ldl = 3;
  ldv = 100;

  d = (lmax+1)*(lmax+2)*(lmax+3)/6

  allocate (L(ldl,d), VGL(ldv,d))

  test_qmckl_ao_polynomial_vgl = &
       qmckl_ao_polynomial_vgl(context, X, R, lmax, n, L, ldl, VGL, ldv)

  if (test_qmckl_ao_polynomial_vgl /= QMCKL_SUCCESS) return
  if (n /= d) return

  do j=1,n
     test_qmckl_ao_polynomial_vgl = QMCKL_FAILURE
     do i=1,3
        if (L(i,j) < 0) return
     end do
     test_qmckl_ao_polynomial_vgl = QMCKL_FAILURE
     if (dabs(1.d0 - VGL(1,j) / (&
          Y(1)**L(1,j) * Y(2)**L(2,j) * Y(3)**L(3,j)  &
          )) > epsilon ) return

     test_qmckl_ao_polynomial_vgl = QMCKL_FAILURE
     if (L(1,j) < 1) then
        if (VGL(2,j) /= 0.d0) return
     else
        if (dabs(1.d0 - VGL(2,j) / (&
             L(1,j) * Y(1)**(L(1,j)-1) * Y(2)**L(2,j) * Y(3)**L(3,j) &
             )) > epsilon ) return
     end if

     test_qmckl_ao_polynomial_vgl = QMCKL_FAILURE
     if (L(2,j) < 1) then
        if (VGL(3,j) /= 0.d0) return
     else
        if (dabs(1.d0 - VGL(3,j) / (&
             L(2,j) * Y(1)**L(1,j) * Y(2)**(L(2,j)-1) * Y(3)**L(3,j) &
             )) > epsilon ) return
     end if

     test_qmckl_ao_polynomial_vgl = QMCKL_FAILURE
     if (L(3,j) < 1) then
        if (VGL(4,j) /= 0.d0) return
     else
        if (dabs(1.d0 - VGL(4,j) / (&
             L(3,j) * Y(1)**L(1,j) * Y(2)**L(2,j) * Y(3)**(L(3,j)-1) &
             )) > epsilon ) return
     end if

     test_qmckl_ao_polynomial_vgl = QMCKL_FAILURE
     w = 0.d0
     if (L(1,j) > 1) then
        w = w + L(1,j) * (L(1,j)-1) * Y(1)**(L(1,j)-2) * Y(2)**L(2,j) * Y(3)**L(3,j)
     end if
     if (L(2,j) > 1) then
        w = w + L(2,j) * (L(2,j)-1) * Y(1)**L(1,j) * Y(2)**(L(2,j)-2) * Y(3)**L(3,j)
     end if
     if (L(3,j) > 1) then
        w = w + L(3,j) * (L(3,j)-1) * Y(1)**L(1,j) * Y(2)**L(2,j) * Y(3)**(L(3,j)-2)
     end if
     if (dabs(1.d0 - VGL(5,j) / w) > epsilon ) return
  end do

  test_qmckl_ao_polynomial_vgl = QMCKL_SUCCESS

  deallocate(L,VGL)
end function test_qmckl_ao_polynomial_vgl
    #+end_src

    #+begin_src c :tangle (eval c_test)
    int  test_qmckl_ao_polynomial_vgl(qmckl_context context);
    assert(0 == test_qmckl_ao_polynomial_vgl(context));
    #+end_src

* Combining radial and polynomial parts
* End of files                                                     :noexport:

  #+begin_src c :tangle (eval h_private_type)
#endif
  #+end_src

*** Test
  #+begin_src c :tangle (eval c_test)
    rc = qmckl_context_destroy(context);
    assert (rc == QMCKL_SUCCESS);

    return 0;
}
  #+end_src

**✸ Compute file names
    #+begin_src emacs-lisp
; The following is required to compute the file names

(setq pwd (file-name-directory buffer-file-name))
(setq name (file-name-nondirectory (substring buffer-file-name 0 -4)))
(setq f  (concat pwd name "_f.f90"))
(setq fh (concat pwd name "_fh.f90"))
(setq c  (concat pwd name ".c"))
(setq h  (concat name ".h"))
(setq h_private  (concat name "_private.h"))
(setq c_test  (concat pwd "test_" name ".c"))
(setq f_test  (concat pwd "test_" name "_f.f90"))

; Minted
(require 'ox-latex)
(setq org-latex-listings 'minted)
(add-to-list 'org-latex-packages-alist '("" "listings"))
(add-to-list 'org-latex-packages-alist '("" "color"))

    #+end_src

    #+RESULTS:
    |   | color    |
    |   | listings |


# -*- mode: org -*-
# vim: syntax=c