program invFSVD_spindet

  BEGIN_DOC
  ! build CI matrix from SVD vectors
  END_DOC

  implicit none

  read_wf = .True.
  TOUCH read_wf

  call run()

end


subroutine run

  implicit none

  integer                       :: mm, nn, i_state, low_rank
  integer                       :: i, j, k, l
  double precision              :: tmp1, eps_det
  double precision, allocatable :: U_SVD(:,:), D_SVD(:), V_SVD(:,:), A_SVD(:,:), US(:,:)
  double precision, allocatable :: newpsi_rows(:), newpsi_columns(:), newpsi_values(:)
  double precision              :: t0, t1, t2
 
  call CPU_TIME(t0)

  i_state = 1
  mm      = n_det_alpha_unique
  nn      = n_det_beta_unique
  print *, ' matrix dimensions:', mm,'x',nn
  print *, ' N det:', N_det

  call ezfio_get_spindeterminants_n_svd_coefs(low_rank)
  print *, ' SVD rank:', low_rank

  allocate( U_SVD(mm,low_rank), D_SVD(low_rank), V_SVD(nn,low_rank) )
  call ezfio_get_spindeterminants_psi_svd_alpha(U_SVD)
  call ezfio_get_spindeterminants_psi_svd_beta (V_SVD)
  call ezfio_get_spindeterminants_psi_svd_coefs(D_SVD)
  print *, ' read EZFIO SVD vectors OK'

  ! US = U x S :
  allocate( US(mm,low_rank) )
  US(:,:) = 0.d0
  do i = 1, mm
    do l = 1, low_rank
      US(i,l) = U_SVD(i,l) * D_SVD(l)
    enddo
  enddo
  print *, ' U x D: ok'
  deallocate( U_SVD , D_SVD )

  ! A_TSVD = US x V.T
  allocate( A_SVD(mm,nn) )
  A_SVD(:,:) = 0.d0
  call dgemm( 'N', 'T', mm, nn, low_rank, 1.d0 &
                , US     , size(US   ,1)       &
                , V_SVD  , size(V_SVD,1)       &
                , 0.d0, A_SVD, size(A_SVD,1)   )
  print *, ' U x D x Vt: ok'
  deallocatE(US)

  call ezfio_set_spindeterminants_n_states(N_states)
  call ezfio_set_spindeterminants_n_det_alpha(n_det_alpha_unique)
  call ezfio_set_spindeterminants_n_det_beta(n_det_beta_unique)

  print *, 'EZFIO set n_det_alpha and n_det_beta'

  ! ---------------
  eps_det = 1d-15 
  print *, ' det coeff thresh for consideration =', eps_det
  ! ---------------


  k = 0
  do j = 1, nn
    do i = 1, mm
      tmp1 = A_SVD(i,j)
      if( dabs(tmp1) .lt. (eps_det) ) cycle      
      k = k + 1
    enddo
  enddo
  print *, ' non zero elements = ', k

  allocate( newpsi_rows(k), newpsi_columns(k), newpsi_values(k) )
  k = 0
  do j = 1, nn
    do i = 1, mm
      tmp1 = A_SVD(i,j)
      if( dabs(tmp1) .lt. (eps_det) ) cycle      
      k                 = k + 1

      newpsi_rows   (k) = i
      newpsi_columns(k) = j
      newpsi_values (k) = tmp1

    enddo
  enddo

  call ezfio_set_spindeterminants_n_det(N_det)
  call ezfio_set_spindeterminants_psi_coef_matrix_columns(psi_bilinear_matrix_columns)
  call ezfio_set_spindeterminants_psi_coef_matrix_values(psi_bilinear_matrix_values)
  call ezfio_set_spindeterminants_psi_coef_matrix_rows(psi_bilinear_matrix_rows)


  deallocate( A_SVD )
  deallocate( newpsi_rows, newpsi_columns, newpsi_values )



  call CPU_TIME(t2)
  print *, ''
  print *, ' end after'
  print *, (t2-t0)/60.d0, 'min'

end