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

All the data relative to the molecular geometry is described here.

* 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_NUCLEUS_HPT
#define QMCKL_NUCLEUS_HPT
#include <stdbool.h>
  #+end_src

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

#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 <math.h>

#include <stdio.h>

#include "qmckl.h"
#include "qmckl_context_private_type.h"
#include "qmckl_memory_private_type.h"
#include "qmckl_memory_private_func.h"
#include "qmckl_nucleus_private_func.h"
  #+end_src

* Context

  The following data stored in the context:

   | ~uninitialized~             | int32_t          | Keeps bit set for uninitialized data                       |
   | ~num~                       | int64_t          | Total number of nuclei                                     |
   | ~provided~                  | bool             | If true, ~nucleus~ is valid                                |
   | ~charge~                    | double[num]      | Nuclear charges                                            |
   | ~coord~                     | double[3][num]   | Nuclear coordinates, in transposed format                  |
   | ~nn_distance~               | double[num][num] | Nucleus-nucleus distances                                  |
   | ~nn_distance_date~          | int64_t          | Date when Nucleus-nucleus distances were computed          |
   | ~nn_distance_rescaled~      | double[num][num] | Nucleus-nucleus rescaled distances                         |
   | ~nn_distance_rescaled_date~ | int64_t          | Date when Nucleus-nucleus rescaled distances were computed |
   | ~repulsion~                 | double           | Nuclear repulsion energy                                   |
   | ~repulsion_date~            | int64_t          | Date when the nuclear repulsion energy was computed        |
   | ~rescale_factor_kappa~      | double           | The distance scaling factor                                |

** Data structure

   #+begin_src c :comments org :tangle (eval h_private_type)
typedef struct qmckl_nucleus_struct {
  int64_t   num;
  int64_t   repulsion_date;
  int64_t   nn_distance_date;
  int64_t   nn_distance_rescaled_date;
  double*   coord;
  double*   charge;
  double*   nn_distance;
  double*   nn_distance_rescaled;
  double    repulsion;
  double    rescale_factor_kappa;
  int32_t   uninitialized;
  bool      provided;
} qmckl_nucleus_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~.

** Access functions
   
   #+begin_src c :comments org :tangle (eval h_func) :exports none
qmckl_exit_code qmckl_get_nucleus_num         (const qmckl_context context, int64_t* const num);
qmckl_exit_code qmckl_get_nucleus_charge      (const qmckl_context context, double* const charge);
qmckl_exit_code qmckl_get_nucleus_kappa       (const qmckl_context context, double* const rescale_factor_kappa);
qmckl_exit_code qmckl_get_nucleus_coord       (const qmckl_context context, const char transp, double* const coord);
   #+end_src

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

   #+begin_src c :comments org :tangle (eval c) :noweb yes :exports none
qmckl_exit_code
qmckl_get_nucleus_num (const qmckl_context context, int64_t* const num) {

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

  if (num == NULL) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_get_nucleus_num",
                           "num is a null pointer");
  }

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

  int32_t mask = 1 << 0;

  if ( (ctx->nucleus.uninitialized & mask) != 0) {
    *num = (int64_t) 0;
    return qmckl_failwith( context,
                           QMCKL_NOT_PROVIDED,
                           "qmckl_get_nucleus_num",
                           "nucleus data is not provided");
  }

  assert (ctx->nucleus.num >= (int64_t) 0);
  ,*num = ctx->nucleus.num;

  return QMCKL_SUCCESS;
}


qmckl_exit_code
qmckl_get_nucleus_charge (const qmckl_context context, double* const charge) {

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

  if (charge == NULL) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_get_nucleus_charge",
                           "charge is a null pointer");
  }

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

  int32_t mask = 1 << 1;

  if ( (ctx->nucleus.uninitialized & mask) != 0) {
    return qmckl_failwith( context,
                           QMCKL_NOT_PROVIDED,
                           "qmckl_get_nucleus_charge",
                           "nucleus data is not provided");
  }

  assert (ctx->nucleus.charge != NULL);

  int64_t nucl_num = ctx->nucleus.num;

  memcpy(charge, ctx->nucleus.charge, nucl_num*sizeof(double));

  return QMCKL_SUCCESS;
}


qmckl_exit_code
qmckl_get_nucleus_kappa (const qmckl_context context, double* const rescale_factor_kappa) {

  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);

  int32_t mask = 1 << 2;

  if ( (ctx->nucleus.uninitialized & mask) != 0) {
    return qmckl_failwith( context,
                           QMCKL_NOT_PROVIDED,
                           "qmckl_get_nucleus_kappa",
                           "nucleus data is not provided");
  }

  (*rescale_factor_kappa) = ctx->nucleus.rescale_factor_kappa;

  return QMCKL_SUCCESS;
}


qmckl_exit_code
qmckl_get_nucleus_coord (const qmckl_context context, const char transp, double* const coord) {
  
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return QMCKL_INVALID_CONTEXT;
  }
  
  if (transp != 'N' && transp != 'T') {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_get_nucleus_coord",
                           "transp should be 'N' or 'T'");
  }

  if (coord == NULL) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_3,
                           "qmckl_get_nucleus_coord",
                           "coord is a null pointer");
  }

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

  int32_t mask = 1 << 3;

  if ( (ctx->nucleus.uninitialized & mask) != 0) {
    return qmckl_failwith( context,
                           QMCKL_NOT_PROVIDED,
                           "qmckl_get_nucleus_coord",
                           "nucleus data is not provided");
  }

  int64_t nucl_num = ctx->nucleus.num;

  assert (ctx->nucleus.coord != NULL);

  if (transp == 'N') {
    qmckl_exit_code rc;

    rc = qmckl_transpose(context, nucl_num, 3,
                         ctx->nucleus.coord, nucl_num,
                         coord, 3);
    if (rc != QMCKL_SUCCESS) return rc;

  } else {

    memcpy(coord, ctx->nucleus.coord, 3*nucl_num*sizeof(double));

  }

  return QMCKL_SUCCESS;
}
   #+end_src

   When all the data relative to nuclei have been set, the following
   function returns ~true~.

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

   #+begin_src c :comments org :tangle (eval c) :noweb yes :exports none
bool qmckl_nucleus_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->nucleus.provided;
}
   #+end_src

** Initialization functions

   To set the data relative to the nuclei in the context, the
   following functions need to be called.

   #+begin_src c :comments org :tangle (eval h_func)
qmckl_exit_code  qmckl_set_nucleus_num    (qmckl_context context, const int64_t num);
qmckl_exit_code  qmckl_set_nucleus_charge (qmckl_context context, const double* charge);
qmckl_exit_code  qmckl_set_nucleus_kappa  (qmckl_context context, const double rescale_factor_kappa);
qmckl_exit_code  qmckl_set_nucleus_coord  (qmckl_context context, const char transp, const double* coord);
   #+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->nucleus.uninitialized &= ~mask;
ctx->nucleus.provided = (ctx->nucleus.uninitialized == 0);

return QMCKL_SUCCESS;
   #+end_src


   To set the number of nuclei, use

   #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code
qmckl_set_nucleus_num(qmckl_context context, const int64_t num) {
  <<pre2>>

  if (num <= 0) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_set_nucleus_num",
                           "num <= 0");
  }

  int32_t mask = 1;

  ctx->nucleus.num = num;

  <<post2>>
}
   #+end_src

    The following function sets the nuclear charges of all the atoms.

   #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code
qmckl_set_nucleus_charge(qmckl_context context, const double* charge) {
  <<pre2>>

  if (charge == NULL) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_set_nucleus_charge",
                           "charge is a null pointer");
  }

  int64_t num;
  qmckl_exit_code rc;

  int32_t mask = 1 << 1;

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

  if (ctx->nucleus.charge != NULL) {
    qmckl_free(context, ctx->nucleus.charge);
    ctx->nucleus.charge= NULL;
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = num*sizeof(double);

  assert (ctx->nucleus.charge == NULL);
  ctx->nucleus.charge = (double*) qmckl_malloc(context, mem_info);
  if (ctx->nucleus.charge == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_nucleus_charge",
                           NULL);
  }
  ctx->nucleus.charge= memcpy(ctx->nucleus.charge, charge, num*sizeof(double));
  assert (ctx->nucleus.charge != NULL);

  <<post2>>
}
    #+end_src
    
    The following function sets the rescale parameter for the nuclear distances.

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

  //TODO: Check for small values of kappa
  //if (rescale_factor_kappa == 0) {
  //  return qmckl_failwith( context,
  //                         QMCKL_INVALID_ARG_2,
  //                         "qmckl_set_nucleus_kappa",
  //                         "rescale_factor_kappa cannot be 0");
  //}

  int32_t mask = 1 << 2;

  int64_t num;
  qmckl_exit_code rc;

  ctx->nucleus.rescale_factor_kappa = rescale_factor_kappa;

  <<post2>>
}
    #+end_src

    The following function sets the nuclear coordinates of all the
    atoms. The coordinates should be given in atomic units.

   #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code
qmckl_set_nucleus_coord(qmckl_context context, const char transp, const double* coord) {
  <<pre2>>

  int64_t nucl_num = (int64_t) 0;
  qmckl_exit_code rc;

  int32_t mask = 1 << 3;

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

  if (ctx->nucleus.coord != NULL) {
    qmckl_free(context, ctx->nucleus.coord);
    ctx->nucleus.coord = NULL;
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = 3*nucl_num*sizeof(double);

  assert(ctx->nucleus.coord == NULL);

  ctx->nucleus.coord = (double*) qmckl_malloc(context, mem_info);
  if (coord == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_nucleus_coord",
                           NULL);
  }
  if (transp == 'N') {
    rc = qmckl_transpose(context, 3, nucl_num,
                         coord, 3,
                         ctx->nucleus.coord, nucl_num);
    if (rc != QMCKL_SUCCESS) return rc;
  } else {
    memcpy(ctx->nucleus.coord, coord, 3*nucl_num*sizeof(double));
  }

  <<post2>>
}
    #+end_src

** Test

    #+begin_src c :tangle (eval c_test)
const int64_t   nucl_num      = chbrclf_nucl_num;
const double*   nucl_charge   = chbrclf_charge;
const double*   nucl_coord    = &(chbrclf_nucl_coord[0][0]);
const double    nucl_rescale_factor_kappa    = 1.0; // TODO Change get rescale_factor_kappa from chbrclf example

/* --- */

qmckl_exit_code rc;

assert(!qmckl_nucleus_provided(context));

int64_t n;
rc = qmckl_get_nucleus_num (context, &n);
assert(rc == QMCKL_NOT_PROVIDED);


rc = qmckl_set_nucleus_num (context, nucl_num);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_nucleus_provided(context));

rc = qmckl_get_nucleus_num (context, &n);
assert(rc == QMCKL_SUCCESS);
assert(n == nucl_num);

double k;
rc = qmckl_get_nucleus_kappa (context, &k);
assert(rc == QMCKL_NOT_PROVIDED);


rc = qmckl_set_nucleus_kappa (context, nucl_rescale_factor_kappa);
assert(rc == QMCKL_SUCCESS);
assert(!qmckl_nucleus_provided(context));

rc = qmckl_get_nucleus_kappa (context, &k);
assert(rc == QMCKL_SUCCESS);
assert(k == nucl_rescale_factor_kappa);

double nucl_coord2[3*nucl_num];

rc = qmckl_get_nucleus_coord (context, 'T', nucl_coord2);
assert(rc == QMCKL_NOT_PROVIDED);

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

assert(!qmckl_nucleus_provided(context));

rc = qmckl_get_nucleus_coord (context, 'N', nucl_coord2);
assert(rc == QMCKL_SUCCESS);
for (size_t k=0 ; k<3 ; ++k) {
  for (size_t i=0 ; i<nucl_num ; ++i) {
    assert( nucl_coord[nucl_num*k+i] == nucl_coord2[3*i+k] );
  }
}

rc = qmckl_get_nucleus_coord (context, 'T', nucl_coord2);
assert(rc == QMCKL_SUCCESS);
for (size_t i=0 ; i<3*nucl_num ; ++i) {
  assert( nucl_coord[i] == nucl_coord2[i] );
}

double nucl_charge2[nucl_num];

rc = qmckl_get_nucleus_charge(context, nucl_charge2);
assert(rc == QMCKL_NOT_PROVIDED);

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

rc = qmckl_get_nucleus_charge(context, nucl_charge2);
assert(rc == QMCKL_SUCCESS);
for (size_t i=0 ; i<nucl_num ; ++i) {
  assert( nucl_charge[i] == nucl_charge2[i] );
 }
assert(qmckl_nucleus_provided(context));
    #+end_src

* Computation

  The computed data is stored in the context so that it can be reused
  by different kernels. To ensure that the data is valid, for each
  computed data the date of the context is stored when it is computed.
  To know if some data needs to be recomputed, we check if the date of
  the dependencies are more recent than the date of the data to
  compute. If it is the case, then the data is recomputed and the
  current date is stored.

** Nucleus-nucleus distances
   
*** Get

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

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_get_nucleus_nn_distance(qmckl_context context, double* distance)
{
  /* Check input parameters */
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return (char) 0;
  }

  qmckl_exit_code rc = qmckl_provide_nn_distance(context);
  if (rc != QMCKL_SUCCESS) return rc;

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

  size_t sze = ctx->nucleus.num * ctx->nucleus.num;
  memcpy(distance, ctx->nucleus.nn_distance, sze * sizeof(double));

  return QMCKL_SUCCESS;
}
    #+end_src

*** Provide                                                        :noexport:

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

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_provide_nn_distance(qmckl_context context)
{
  /* Check input parameters */
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return (char) 0;
  }

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

  if (!ctx->nucleus.provided) return QMCKL_NOT_PROVIDED;

  /* Allocate array */
  if (ctx->nucleus.nn_distance == NULL) {

    qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
    mem_info.size = ctx->nucleus.num * ctx->nucleus.num * sizeof(double);
    double* nn_distance = (double*) qmckl_malloc(context, mem_info);

    if (nn_distance == NULL) {
      return qmckl_failwith( context,
                             QMCKL_ALLOCATION_FAILED,
                             "qmckl_nn_distance",
                             NULL);
    }
    ctx->nucleus.nn_distance = nn_distance;
  }

  qmckl_exit_code rc =
    qmckl_compute_nn_distance(context,
                              ctx->nucleus.num,
                              ctx->nucleus.coord,
                              ctx->nucleus.nn_distance);
  if (rc != QMCKL_SUCCESS) {
    return rc;
  }

  ctx->nucleus.nn_distance_date = ctx->date;

  return QMCKL_SUCCESS;
}
    #+end_src

*** Compute

    #+NAME: qmckl_nn_distance_args
   | qmckl_context | context                         | in  | Global state                   |
   | int64_t       | nucl_num                        | in  | Number of nuclei               |
   | double        | coord[3][nucl_num]              | in  | Nuclear coordinates (au)       |
   | double        | nn_distance[nucl_num][nucl_num] | out | Nucleus-nucleus distances (au) |

    #+begin_src f90 :comments org :tangle (eval f) :noweb yes
integer function qmckl_compute_nn_distance_f(context, nucl_num, coord, nn_distance) &
     result(info)
  use qmckl
  implicit none
  integer(qmckl_context), intent(in)  :: context
  integer*8             , intent(in)  :: nucl_num
  double precision      , intent(in)  :: coord(nucl_num,3)
  double precision      , intent(out) :: nn_distance(nucl_num,nucl_num)

  integer*8 :: k

  info = QMCKL_SUCCESS

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

  if (nucl_num <= 0) then
     info = QMCKL_INVALID_ARG_2
     return
  endif

  info = qmckl_distance(context, 'T', 'T', nucl_num, nucl_num, &
          coord, nucl_num, &
          coord, nucl_num, &
          nn_distance, nucl_num)

end function qmckl_compute_nn_distance_f
    #+end_src

    #+begin_src c :tangle (eval h_private_func) :comments org :exports none
qmckl_exit_code qmckl_compute_nn_distance (
          const qmckl_context context,
          const int64_t nucl_num,
          const double* coord,
          double* const nn_distance );
    #+end_src


    #+CALL: generate_c_interface(table=qmckl_nn_distance_args,rettyp="qmckl_exit_code",fname="qmckl_compute_nn_distance")

    #+RESULTS:
    #+begin_src f90 :tangle (eval f) :comments org :exports none
    integer(c_int32_t) function qmckl_compute_nn_distance &
        (context, nucl_num, coord, nn_distance) &
        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 :: nucl_num
      real    (c_double ) , intent(in)          :: coord(nucl_num,3)
      real    (c_double ) , intent(out)         :: nn_distance(nucl_num,nucl_num)

      integer(c_int32_t), external :: qmckl_compute_nn_distance_f
      info = qmckl_compute_nn_distance_f &
             (context, nucl_num, coord, nn_distance)

    end function qmckl_compute_nn_distance
    #+end_src

*** Test

     #+begin_src c :tangle (eval c_test)
/* Reference input data */

assert(qmckl_nucleus_provided(context));

double distance[nucl_num*nucl_num];
rc = qmckl_get_nucleus_nn_distance(context, distance);
assert(distance[0] == 0.);
assert(distance[1] == distance[nucl_num]);
assert(fabs(distance[1]-2.070304721365169) < 1.e-12);

     #+end_src


** Nucleus-nucleus rescaled distances

*** Get

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

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_get_nucleus_nn_distance_rescaled(qmckl_context context, double* distance_rescaled)
{
  /* Check input parameters */
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return (char) 0;
  }

  qmckl_exit_code rc = qmckl_provide_nn_distance_rescaled(context);
  if (rc != QMCKL_SUCCESS) return rc;

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

  size_t sze = ctx->nucleus.num * ctx->nucleus.num;
  memcpy(distance_rescaled, ctx->nucleus.nn_distance_rescaled, sze * sizeof(double));

  return QMCKL_SUCCESS;
}
    #+end_src

*** Provide                                                        :noexport:

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

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_provide_nn_distance_rescaled(qmckl_context context)
{
  /* Check input parameters */
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return (char) 0;
  }

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

  if (!ctx->nucleus.provided) return QMCKL_NOT_PROVIDED;

  /* Allocate array */
  if (ctx->nucleus.nn_distance_rescaled == NULL) {

    qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
    mem_info.size = ctx->nucleus.num * ctx->nucleus.num * sizeof(double);
    double* nn_distance_rescaled = (double*) qmckl_malloc(context, mem_info);

    if (nn_distance_rescaled == NULL) {
      return qmckl_failwith( context,
                             QMCKL_ALLOCATION_FAILED,
                             "qmckl_nn_distance_rescaled",
                             NULL);
    }
    ctx->nucleus.nn_distance_rescaled = nn_distance_rescaled;
  }

  qmckl_exit_code rc =
    qmckl_compute_nn_distance_rescaled(context,
                              ctx->nucleus.num,
                              ctx->nucleus.rescale_factor_kappa,
                              ctx->nucleus.coord,
                              ctx->nucleus.nn_distance_rescaled);
  if (rc != QMCKL_SUCCESS) {
    return rc;
  }

  ctx->nucleus.nn_distance_rescaled_date = ctx->date;

  return QMCKL_SUCCESS;
}
    #+end_src

*** Compute

    #+NAME: qmckl_nn_distance_rescaled_args
   | qmckl_context | context                                  | in  | Global state                            |
   | int64_t       | nucl_num                                 | in  | Number of nuclei                        |
   | double        | coord[3][nucl_num]                       | in  | Nuclear coordinates (au)                |
   | double        | nn_distance_rescaled[nucl_num][nucl_num] | out | Nucleus-nucleus rescaled distances (au) |

    #+begin_src f90 :comments org :tangle (eval f) :noweb yes
integer function qmckl_compute_nn_distance_rescaled_f(context, nucl_num, rescale_factor_kappa, coord, nn_distance_rescaled) &
     result(info)
  use qmckl
  implicit none
  integer(qmckl_context), intent(in)  :: context
  integer*8             , intent(in)  :: nucl_num
  double precision      , intent(in)  :: rescale_factor_kappa
  double precision      , intent(in)  :: coord(nucl_num,3)
  double precision      , intent(out) :: nn_distance_rescaled(nucl_num,nucl_num)

  integer*8 :: k

  info = QMCKL_SUCCESS

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

  if (nucl_num <= 0) then
     info = QMCKL_INVALID_ARG_2
     return
  endif

  info = qmckl_distance_rescaled(context, 'T', 'T', nucl_num, nucl_num, &
          coord, nucl_num, &
          coord, nucl_num, &
          nn_distance_rescaled, nucl_num, rescale_factor_kappa)

end function qmckl_compute_nn_distance_rescaled_f
    #+end_src

    #+begin_src c :tangle (eval h_private_func) :comments org :exports none
qmckl_exit_code qmckl_compute_nn_distance_rescaled (
          const qmckl_context context,
          const int64_t nucl_num,
          const double  rescale_factor_kappa,
          const double* coord,
          double* const nn_distance_rescaled );
    #+end_src


    #+CALL: generate_c_interface(table=qmckl_nn_distance_rescaled_args,rettyp="qmckl_exit_code",fname="qmckl_compute_nn_distance")

    #+RESULTS:
    #+begin_src f90 :tangle (eval f) :comments org :exports none
    integer(c_int32_t) function qmckl_compute_nn_distance_rescaled &
        (context, nucl_num, rescale_factor_kappa, coord, nn_distance_rescaled) &
        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 :: nucl_num
      real    (c_double ) , intent(in)  , value :: rescale_factor_kappa
      real    (c_double ) , intent(in)          :: coord(nucl_num,3)
      real    (c_double ) , intent(out)         :: nn_distance_rescaled(nucl_num,nucl_num)

      integer(c_int32_t), external :: qmckl_compute_nn_distance_rescaled_f
      info = qmckl_compute_nn_distance_rescaled_f &
             (context, nucl_num, rescale_factor_kappa, coord, nn_distance_rescaled)

    end function qmckl_compute_nn_distance_rescaled
    #+end_src

*** Test

     #+begin_src c :tangle (eval c_test)
/* Reference input data */
/* TODO */

//assert(qmckl_nucleus_provided(context));
//
//double distance[nucl_num*nucl_num];
//rc = qmckl_get_nucleus_nn_distance(context, distance);
//assert(distance[0] == 0.);
//assert(distance[1] == distance[nucl_num]);
//assert(fabs(distance[1]-2.070304721365169) < 1.e-12);

     #+end_src

** Nuclear repulsion energy

   \[
   V_{NN} = \sum_{A=1}^{N-1} \sum_{B>A}^N \frac{Q_A Q_B}{R_{AB}}
   \]

*** Get
    
    #+begin_src c :comments org :tangle (eval h_func) :noweb yes
qmckl_exit_code qmckl_get_nucleus_repulsion(qmckl_context context, double* energy);
    #+end_src

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_get_nucleus_repulsion(qmckl_context context, double* energy)
{
  /* Check input parameters */
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return (char) 0;
  }

  qmckl_exit_code rc = qmckl_provide_nucleus_repulsion(context);
  if (rc != QMCKL_SUCCESS) return rc;

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

  *energy = ctx->nucleus.repulsion;

  return QMCKL_SUCCESS;
}
    #+end_src

*** Provide                                                        :noexport:

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

    #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none
qmckl_exit_code qmckl_provide_nucleus_repulsion(qmckl_context context)
{
  /* Check input parameters */
  if (qmckl_context_check(context) == QMCKL_NULL_CONTEXT) {
    return (char) 0;
  }

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

  qmckl_exit_code rc;

  if (!ctx->nucleus.provided) return QMCKL_NOT_PROVIDED;

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

  rc = qmckl_compute_nucleus_repulsion(context,
                                ctx->nucleus.num,
                                ctx->nucleus.charge,
                                ctx->nucleus.nn_distance,
                                &(ctx->nucleus.repulsion));
  if (rc != QMCKL_SUCCESS) {
    return rc;
    }

  ctx->nucleus.repulsion_date = ctx->date;

  return QMCKL_SUCCESS;
}
    #+end_src

*** Compute

    #+NAME: qmckl_nucleus_repulsion_args
   | qmckl_context | context                         | in  | Global state                   |
   | int64_t       | nucl_num                        | in  | Number of nuclei               |
   | double        | charge[nucl_num]                | in  | Nuclear charges (au)           |
   | double        | nn_distance[nucl_num][nucl_num] | in  | Nucleus-nucleus distances (au) |
   | double        | energy                          | out | Nuclear repulsion energy       |

    #+begin_src f90 :comments org :tangle (eval f) :noweb yes
integer function qmckl_compute_nucleus_repulsion_f(context, nucl_num, charge, nn_distance, energy) &
     result(info)
  use qmckl
  implicit none
  integer(qmckl_context), intent(in)  :: context
  integer*8             , intent(in)  :: nucl_num
  double precision      , intent(in)  :: charge(nucl_num)
  double precision      , intent(in)  :: nn_distance(nucl_num,nucl_num)
  double precision      , intent(out) :: energy

  integer*8 :: i, j

  info = QMCKL_SUCCESS

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

  if (nucl_num <= 0) then
     info = QMCKL_INVALID_ARG_2
     return
  endif

  energy = 0.d0
  do j=2, nucl_num
     do i=1, j-1
        energy = energy + charge(i) * charge(j) / nn_distance(i,j)
     end do
  end do

end function qmckl_compute_nucleus_repulsion_f
    #+end_src

    #+begin_src c :tangle (eval h_private_func) :comments org :exports none
qmckl_exit_code qmckl_compute_nucleus_repulsion (
     const qmckl_context context,
     const int64_t nucl_num,
     const double* charge,
     const double* nn_distance,
     double* energy
  );
    #+end_src

    #+CALL: generate_c_interface(table=qmckl_nucleus_repulsion_args,rettyp="qmckl_exit_code",fname="qmckl_compute_nucleus_repulsion")

    #+RESULTS:
    #+begin_src f90 :tangle (eval f) :comments org :exports none
    integer(c_int32_t) function qmckl_compute_nucleus_repulsion &
        (context, nucl_num, charge, nn_distance, energy) &
        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 :: nucl_num
      real    (c_double ) , intent(in)          :: charge(nucl_num)
      real    (c_double ) , intent(in)          :: nn_distance(nucl_num,nucl_num)
      real    (c_double ) , intent(out)         :: energy

      integer(c_int32_t), external :: qmckl_compute_nucleus_repulsion_f
      info = qmckl_compute_nucleus_repulsion_f &
             (context, nucl_num, charge, nn_distance, energy)

    end function qmckl_compute_nucleus_repulsion
    #+end_src

*** Test

     #+begin_src c :tangle (eval c_test)
/* Reference input data */

assert(qmckl_nucleus_provided(context));

double rep;
rc = qmckl_get_nucleus_repulsion(context, &rep);
assert(rep - 318.2309879436158 < 1.e-10);

     #+end_src

* End of files                                                     :noexport:

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

*** Test
  #+begin_src c :tangle (eval c_test)
  if (qmckl_context_destroy(context) != QMCKL_SUCCESS)
    return QMCKL_FAILURE;
  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:


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