* Debug the gradient

*Program to check the gradient*

The program compares the result of the first and last code for the
gradient.

Provided:
| mo_num | integer | number of MOs |

Internal:
| n          | integer          | number of orbitals pairs (p,q) p<q |
| v_grad(n)  | double precision | Original gradient                  |
| v_grad2(n) | double precision | Gradient                           |
| i          | integer          | index                              |
| threshold  | double precision | threshold for the errors           |
| max_error  | double precision | maximal error in the gradient      |
| nb_error   | integer          | number of error in the gradient    |

#+BEGIN_SRC f90 :comments org :tangle debug_gradient_opt.irp.f
program debug_gradient
  
  implicit none

  ! Variables

  double precision, allocatable :: v_grad(:), v_grad2(:)
  integer                       :: n
  integer                       :: i
  double precision              :: threshold
  double precision              :: max_error, max_elem
  integer                       :: nb_error
  
  ! Definition of n  
  n = mo_num*(mo_num-1)/2

  PROVIDE mo_two_e_integrals_in_map ! Vérifier pour suppression

  ! Allocation
  allocate(v_grad(n), v_grad2(n))

  ! Calculation

  call diagonalize_ci ! Vérifier pour suppression

  ! Gradient  
  call first_gradient_opt(n,v_grad)
  call gradient_opt(n,v_grad2,max_elem)
  
  v_grad = v_grad - v_grad2
  nb_error = 0
  max_error = 0d0 
  threshold = 1d-12 

  do i = 1, n
    if (ABS(v_grad(i)) > threshold) then
       print*,v_grad(i)
       nb_error = nb_error + 1

       if (ABS(v_grad(i)) > max_error) then
         max_error = v_grad(i)
       endif

    endif
  enddo
 
  print*,''
  print*,'Check the gradient' 
  print*,'Threshold :', threshold
  print*,'Nb error :', nb_error
  print*,'Max error :', max_error

  ! Deallocation
  deallocate(v_grad,v_grad2)

end program
#+END_SRC