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

In conventional QMC simulations, up-spin and down-spin electrons are
different. The ~electron~  data structure contains the number of
up-spin and down-spin electrons, and the electron coordinates.

* 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_ELECTRON_HPT
#define QMCKL_ELECTRON_HPT
#include <stdbool.h>
  #+end_src

  #+begin_src c :tangle (eval c_test) :noweb yes
#include "qmckl.h"
#include "munit.h"
MunitResult test_<<filename()>>() {
  qmckl_context context;
  context = qmckl_context_create();
  #+end_src

  #+begin_src c :tangle (eval c)
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <assert.h>

#include "qmckl_error_type.h"
#include "qmckl_context_type.h"
#include "qmckl_context_private_type.h"
#include "qmckl_memory_private_type.h"

#include "qmckl_error_func.h"
#include "qmckl_memory_private_func.h"
#include "qmckl_memory_func.h"
#include "qmckl_context_func.h"
  #+end_src

* Context

  The following data stored in the context:
 
   | ~date~          | uint64_t                 | Last modification date of the coordinates |
   | ~uninitialized~ | int32_t                  | Keeps bit set for uninitialized data      |
   | ~num~           | int64_t                  | Total number of electrons                 |
   | ~up_num~        | int64_t                  | Number of up-spin electrons               |
   | ~down_num~      | int64_t                  | Number of down-spin electrons             |
   | ~walk_num~      | int64_t                  | Number of walkers                         |
   | ~provided~      | bool                     | If true, ~electron~ is valid              |
   | ~coord_new~     | double[walk_num][3][num] | New set of electron coordinates           |
   | ~coord_old~     | double[walk_num][3][num] | Old set of electron coordinates           |

** Data structure

   #+begin_src c :comments org :tangle (eval h_private_type)
typedef struct qmckl_electron_struct {
  int64_t   date;
  int64_t   num;
  int64_t   up_num;
  int64_t   down_num;
  int64_t   walk_num;
  double*   coord_new;
  double*   coord_old;
  int32_t   uninitialized;
  bool      provided;
} qmckl_electron_struct;
   #+end_src

   The ~uninitialized~ integer contains one bit set to one for each
   initialization function which has not bee 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_private_func) :exports none
int64_t   qmckl_get_electron_num        (const qmckl_context context);
int64_t   qmckl_get_electron_up_num     (const qmckl_context context);
int64_t   qmckl_get_electron_down_num   (const qmckl_context context);
int64_t   qmckl_get_electron_walk_num   (const qmckl_context context);
double*   qmckl_get_electron_coord_new  (const qmckl_context context);
double*   qmckl_get_electron_coord_old  (const qmckl_context context);
   #+end_src

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

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

   #+NAME:post
   #+begin_src c  :exports none
if ( (ctx->electron.uninitialized & mask) != 0) {
  return NULL;
}
   #+end_src
   
   #+begin_src c :comments org :tangle (eval c) :noweb yes :exports none
int64_t qmckl_get_electron_num (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->electron.uninitialized & mask) != 0) {
    return (int64_t) 0;
  }

  assert (ctx->electron.num > (int64_t) 0);
  return ctx->electron.num;
}


int64_t qmckl_get_electron_up_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->electron.uninitialized & mask) != 0) {
    return (int64_t) 0;
  }

  assert (ctx->electron.up_num > (int64_t) 0);
  return ctx->electron.up_num;
}


int64_t qmckl_get_electron_down_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->electron.uninitialized & mask) != 0) {
    return (int64_t) 0;
  }

  assert (ctx->electron.down_num >= (int64_t) 0);
  return ctx->electron.down_num;
}


int64_t qmckl_get_electron_walk_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 << 3;

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

  assert (ctx->electron.walk_num > (int64_t) 0);
  return ctx->electron.walk_num;
}



bool qmckl_electron_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->electron.provided;
}
   #+end_src
   
** Initialization functions

   To set the data relative to the electrons in the context, the
   following functions need to be called. When the data structure is
   initialized, the ~coord_new~ and ~coord_old~ arrays are both allocated.
   
   #+begin_src c :comments org :tangle (eval h_func)
qmckl_exit_code  qmckl_set_electron_num        (qmckl_context context, const int64_t up_num, const int64_t down_num);
qmckl_exit_code  qmckl_set_electron_walk_num   (qmckl_context context, const int64_t walk_num);
qmckl_exit_code  qmckl_set_electron_coord      (qmckl_context context, 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->electron.uninitialized &= ~mask; 
ctx->electron.provided = (ctx->electron.uninitialized == 0);

if (ctx->electron.provided) {
  if (ctx->electron.coord_new != NULL) {
    qmckl_free(context, ctx->electron.coord_new);
    ctx->electron.coord_new = NULL;
  }
  if (ctx->electron.coord_old != NULL) {
    qmckl_free(context, ctx->electron.coord_old);
    ctx->electron.coord_old = NULL;
  }

  qmckl_memory_info_struct mem_info = qmckl_memory_info_struct_zero;
  mem_info.size = ctx->electron.num * ctx->electron.walk_num * 3 * sizeof(double);

  double* coord_new = (double*) qmckl_malloc(context, mem_info);
  if (coord_new == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_electron_num",
                           NULL);
  }
  ctx->electron.coord_new = coord_new;

  double* coord_old = (double*) qmckl_malloc(context, mem_info);
  if (coord_old == NULL) {
    return qmckl_failwith( context,
                           QMCKL_ALLOCATION_FAILED,
                           "qmckl_set_electron_num",
                           NULL);
  }
  ctx->electron.coord_old = coord_old;
 }

return QMCKL_SUCCESS;
   #+end_src
   
   To set the number of electrons, we give the number of up-spin and
   down-spin electrons to the context and we set the number of walkers.
   
   #+begin_src c :comments org :tangle (eval c) :noweb yes  :exports none 
qmckl_exit_code qmckl_set_electron_num(qmckl_context context,
                                       const int64_t up_num,
                                       const int64_t down_num) {
  <<pre2>>

  if (up_num <= 0) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_set_electron_num",
                           "up_num <= 0");
  }

  if (down_num <= 0) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_3,
                           "qmckl_set_electron_num",
                           "down_num <= 0");
  }

  int32_t mask = (1 << 3) -1;

  ctx->electron.up_num = up_num;
  ctx->electron.down_num = down_num;
  ctx->electron.num = up_num + down_num;

  <<post2>>
}
   #+end_src
 
 
   #+begin_src c :comments org :tangle (eval c) :noweb yes :exports none 
qmckl_exit_code qmckl_set_electron_walk_num(qmckl_context context, const int64_t walk_num) {
  <<pre2>>

  if (walk_num <= 0) {
    return qmckl_failwith( context,
                           QMCKL_INVALID_ARG_2,
                           "qmckl_set_electron_walk_num",
                           "walk_num <= 0");
  }

  int32_t mask = 1 << 3;
  ctx->electron.walk_num = walk_num;

  <<post2>>
}
    #+end_src
 
 
    The following function sets the electron coordinates of all the
    walkers. When this is done, the pointers to the old and new sets
    of coordinates are swapped, and the new coordinates are
    overwritten. This can be done only when the data relative to
    electrons have been set.
    
   #+begin_src c :comments org :tangle (eval c) :noweb yes :exports none
qmckl_exit_code  qmckl_set_electron_coord(qmckl_context context, const double* coord) {
  <<pre2>>

  const int64_t num = qmckl_get_electron_num(context);
  if (num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_electron_coord",
                           "num is not set");
  }
    
  const int64_t walk_num = qmckl_get_electron_walk_num(context);
  if (walk_num == 0L) {
    return qmckl_failwith( context,
                           QMCKL_FAILURE,
                           "qmckl_set_electron_coord",
                           "walk_num is not set");
  }
    
  /* If num and walk_num are set, the arrays should be allocated */
  assert (ctx->electron.coord_old != NULL);
  assert (ctx->electron.coord_new != NULL);
  
  /* Increment the date of the context */
  ctx->date += 1UL;

  /* Swap pointers */
  double * swap;
  swap = ctx->electron.coord_old;
  ctx->electron.coord_old = ctx->electron.coord_new;
  ctx->electron.coord_new = swap;
  
  memcpy(ctx->electron.coord_new, coord, walk_num * num * 3 * sizeof(double));
  ctx->electron.date = ctx->date;

  return QMCKL_SUCCESS;
    
}
   #+end_src

** Test

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

#define up_num      ((int64_t) 3)
#define down_num    ((int64_t) 2)
#define walk_num    ((int64_t) 2)
#define num         (up_num+down_num)

double coord[walk_num*3*num] =
  { 7.303633091022677881e+00, 1.375868694453235719e+01, 1.167371490471771217e-01,                   
    4.547755371567960836e+00, 3.245907105524011182e+00, 2.410764357550297110e-01,
    5.932816068137344523e+00, 1.491671465549257469e+01, 3.825374039119375236e-01,
    7.347336142660052083e+00, 1.341946976062362129e+00, 1.648917914228352322e+00,
    5.735221530102248444e+00, 1.064667491680036271e+01, 4.227201772236627297e-01,
    8.099550978782254163e+00, 6.861498941099086757e+00, 4.015884841159429036e-02,
    1.014757367558326173e+01, 5.219335322173662917e+00, 5.037004126899931322e-02,
    1.484094322159507051e+01, 9.777903829455864226e+00, 5.243007994024882767e-02,
    9.081723054990456845e+00, 5.499568496038920173e+00, 2.910446438899221347e-02,
    2.583154239492383653e+00, 1.442282811294904432e+00, 6.387191629878670451e-02 };
  
/* --- */
  
qmckl_exit_code rc;

munit_assert(!qmckl_electron_provided(context));

rc = qmckl_set_electron_num (context, up_num, down_num);
munit_assert_int64(rc, ==, QMCKL_SUCCESS);
munit_assert(!qmckl_electron_provided(context));

rc = qmckl_set_electron_walk_num (context, walk_num);
munit_assert_int64(rc, ==, QMCKL_SUCCESS);
munit_assert(qmckl_electron_provided(context));

rc = qmckl_set_electron_coord (context, coord);
munit_assert_int64(rc, ==, QMCKL_SUCCESS);

    #+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 MUNIT_OK;
}
  #+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