!--------------------------------------------------------------------------------------------------!
!   CP2K: A general program to perform molecular dynamics simulations                              !
!   Copyright 2000-2025 CP2K developers group <https://cp2k.org>                                   !
!                                                                                                  !
!   SPDX-License-Identifier: GPL-2.0-or-later                                                      !
!--------------------------------------------------------------------------------------------------!

! **************************************************************************************************
!> \brief Subroutines to handle submatrices
!> \par History
!>       2013.01 created [Rustam Z Khaliullin]
!> \author Rustam Z Khaliullin
! **************************************************************************************************
MODULE domain_submatrix_methods

   USE cp_dbcsr_api,                    ONLY: &
        dbcsr_distribution_get, dbcsr_distribution_type, dbcsr_filter, dbcsr_finalize, &
        dbcsr_get_block_p, dbcsr_get_info, dbcsr_get_matrix_type, dbcsr_get_stored_coordinates, &
        dbcsr_iterator_blocks_left, dbcsr_iterator_next_block, dbcsr_iterator_start, &
        dbcsr_iterator_stop, dbcsr_iterator_type, dbcsr_nblkcols_total, dbcsr_nblkrows_total, &
        dbcsr_reserve_block2d, dbcsr_type, dbcsr_type_antisymmetric, dbcsr_type_no_symmetry, &
        dbcsr_type_symmetric, dbcsr_work_create
   USE cp_log_handling,                 ONLY: cp_get_default_logger,&
                                              cp_logger_get_default_unit_nr,&
                                              cp_logger_type
   USE domain_submatrix_types,          ONLY: domain_map_type,&
                                              domain_submatrix_type,&
                                              select_row_col
   USE kinds,                           ONLY: dp
   USE message_passing,                 ONLY: mp_comm_null,&
                                              mp_comm_type
#include "./base/base_uses.f90"

   IMPLICIT NONE

   PRIVATE

   CHARACTER(len=*), PARAMETER, PRIVATE :: moduleN = 'domain_submatrix_methods'

   PUBLIC :: copy_submatrices, copy_submatrix_data, &
             release_submatrices, multiply_submatrices, add_submatrices, &
             construct_submatrices, init_submatrices, &
             construct_dbcsr_from_submatrices, &
             set_submatrices, &
             print_submatrices, maxnorm_submatrices

   INTERFACE init_submatrices
      MODULE PROCEDURE init_submatrices_0d
      MODULE PROCEDURE init_submatrices_1d
      MODULE PROCEDURE init_submatrices_2d
   END INTERFACE

   INTERFACE set_submatrices
      MODULE PROCEDURE set_submatrix_array
      MODULE PROCEDURE set_submatrix
   END INTERFACE

   INTERFACE copy_submatrices
      MODULE PROCEDURE copy_submatrix_array
      MODULE PROCEDURE copy_submatrix
   END INTERFACE

   INTERFACE release_submatrices
      MODULE PROCEDURE release_submatrix_array
      MODULE PROCEDURE release_submatrix
   END INTERFACE

   INTERFACE multiply_submatrices
      MODULE PROCEDURE multiply_submatrices_once
      MODULE PROCEDURE multiply_submatrices_array
   END INTERFACE

   INTERFACE add_submatrices
      MODULE PROCEDURE add_submatrices_once
      MODULE PROCEDURE add_submatrices_array
   END INTERFACE

CONTAINS

! **************************************************************************************************
!> \brief ...
!> \param subm ...
! **************************************************************************************************
   SUBROUTINE init_submatrices_0d(subm)

      TYPE(domain_submatrix_type), INTENT(INOUT)         :: subm

      subm%domain = -1
      subm%nbrows = -1
      subm%nbcols = -1
      subm%nrows = -1
      subm%ncols = -1
      subm%nnodes = -1
      subm%group = mp_comm_null

   END SUBROUTINE init_submatrices_0d

! **************************************************************************************************
!> \brief ...
!> \param subm ...
! **************************************************************************************************
   SUBROUTINE init_submatrices_1d(subm)

      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(INOUT)                                   :: subm

      subm(:)%domain = -1
      subm(:)%nbrows = -1
      subm(:)%nbcols = -1
      subm(:)%nrows = -1
      subm(:)%ncols = -1
      subm(:)%nnodes = -1
      subm(:)%group = mp_comm_null

   END SUBROUTINE init_submatrices_1d

! **************************************************************************************************
!> \brief ...
!> \param subm ...
! **************************************************************************************************
   SUBROUTINE init_submatrices_2d(subm)

      TYPE(domain_submatrix_type), DIMENSION(:, :), &
         INTENT(INOUT)                                   :: subm

      subm(:, :)%domain = -1
      subm(:, :)%nbrows = -1
      subm(:, :)%nbcols = -1
      subm(:, :)%nrows = -1
      subm(:, :)%ncols = -1
      subm(:, :)%nnodes = -1
      subm(:, :)%group = mp_comm_null

   END SUBROUTINE init_submatrices_2d

! **************************************************************************************************
!> \brief ...
!> \param original ...
!> \param copy ...
!> \param copy_data ...
! **************************************************************************************************
   SUBROUTINE copy_submatrix_array(original, copy, copy_data)

      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(IN)                                      :: original
      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(INOUT)                                   :: copy
      LOGICAL, INTENT(IN)                                :: copy_data

      CHARACTER(len=*), PARAMETER :: routineN = 'copy_submatrix_array'

      INTEGER                                            :: handle, idomain, ndomains, ndomainsB

      CALL timeset(routineN, handle)

      ndomains = SIZE(original)
      ndomainsB = SIZE(copy)
      CPASSERT(ndomains .EQ. ndomainsB)
      copy(:)%nnodes = original(:)%nnodes
      copy(:)%group = original(:)%group
      DO idomain = 1, ndomains
         IF (original(idomain)%domain .GT. 0) THEN
            CALL copy_submatrix(original(idomain), copy(idomain), copy_data)
         END IF
      END DO ! loop over domains

      CALL timestop(handle)

   END SUBROUTINE copy_submatrix_array

! **************************************************************************************************
!> \brief ...
!> \param original ...
!> \param copy ...
!> \param copy_data ...
! **************************************************************************************************
   SUBROUTINE copy_submatrix(original, copy, copy_data)

      TYPE(domain_submatrix_type), INTENT(IN)            :: original
      TYPE(domain_submatrix_type), INTENT(INOUT)         :: copy
      LOGICAL, INTENT(IN)                                :: copy_data

      CHARACTER(len=*), PARAMETER                        :: routineN = 'copy_submatrix'

      INTEGER                                            :: handle, icol, irow

      CALL timeset(routineN, handle)

      copy%domain = original%domain
      copy%nnodes = original%nnodes
      copy%group = original%group

      IF (original%domain .GT. 0) THEN

         copy%nbrows = original%nbrows
         copy%nbcols = original%nbcols
         copy%nrows = original%nrows
         copy%ncols = original%ncols

         IF (.NOT. ALLOCATED(copy%dbcsr_row)) THEN
            ALLOCATE (copy%dbcsr_row(original%nbrows))
         ELSE
            IF (SIZE(copy%dbcsr_row) .NE. SIZE(original%dbcsr_row)) THEN
               DEALLOCATE (copy%dbcsr_row)
               ALLOCATE (copy%dbcsr_row(original%nbrows))
            END IF
         END IF
         IF (.NOT. ALLOCATED(copy%dbcsr_col)) THEN
            ALLOCATE (copy%dbcsr_col(original%nbcols))
         ELSE
            IF (SIZE(copy%dbcsr_col) .NE. SIZE(original%dbcsr_col)) THEN
               DEALLOCATE (copy%dbcsr_col)
               ALLOCATE (copy%dbcsr_col(original%nbcols))
            END IF
         END IF
         IF (.NOT. ALLOCATED(copy%size_brow)) THEN
            ALLOCATE (copy%size_brow(original%nbrows))
         ELSE
            IF (SIZE(copy%size_brow) .NE. SIZE(original%size_brow)) THEN
               DEALLOCATE (copy%size_brow)
               ALLOCATE (copy%size_brow(original%nbrows))
            END IF
         END IF
         IF (.NOT. ALLOCATED(copy%size_bcol)) THEN
            ALLOCATE (copy%size_bcol(original%nbcols))
         ELSE
            IF (SIZE(copy%size_bcol) .NE. SIZE(original%size_bcol)) THEN
               DEALLOCATE (copy%size_bcol)
               ALLOCATE (copy%size_bcol(original%nbcols))
            END IF
         END IF

         DO irow = 1, original%nbrows
            copy%dbcsr_row(irow) = original%dbcsr_row(irow)
            copy%size_brow(irow) = original%size_brow(irow)
         END DO

         DO icol = 1, original%nbcols
            copy%dbcsr_col(icol) = original%dbcsr_col(icol)
            copy%size_bcol(icol) = original%size_bcol(icol)
         END DO

         IF (copy_data) THEN
            CALL copy_submatrix_data(original%mdata, copy)
         END IF

      END IF ! do not copy empty submatrix

      CALL timestop(handle)

   END SUBROUTINE copy_submatrix

! **************************************************************************************************
!> \brief ...
!> \param array ...
!> \param copy ...
! **************************************************************************************************
   SUBROUTINE copy_submatrix_data(array, copy)

      REAL(KIND=dp), DIMENSION(:, :), INTENT(IN)         :: array
      TYPE(domain_submatrix_type), INTENT(INOUT)         :: copy

      CHARACTER(len=*), PARAMETER :: routineN = 'copy_submatrix_data'

      INTEGER                                            :: ds1, ds2, handle, ms1, ms2

      CALL timeset(routineN, handle)

      CPASSERT(copy%domain .GT. 0)

      ds1 = SIZE(array, 1)
      ds2 = SIZE(array, 2)

      IF (.NOT. ALLOCATED(copy%mdata)) THEN
         ALLOCATE (copy%mdata(ds1, ds2))
      ELSE
         ms1 = SIZE(copy%mdata, 1)
         ms2 = SIZE(copy%mdata, 2)
         IF ((ds1 .NE. ms1) .OR. (ds2 .NE. ms2)) THEN
            DEALLOCATE (copy%mdata)
            ALLOCATE (copy%mdata(ds1, ds2))
         END IF
      END IF

      copy%mdata(:, :) = array(:, :)

      CALL timestop(handle)

   END SUBROUTINE copy_submatrix_data

! **************************************************************************************************
!> \brief ...
!> \param submatrices ...
!> \param scalar ...
! **************************************************************************************************
   SUBROUTINE set_submatrix_array(submatrices, scalar)

      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(INOUT)                                   :: submatrices
      REAL(KIND=dp), INTENT(IN)                          :: scalar

      CHARACTER(len=*), PARAMETER :: routineN = 'set_submatrix_array'

      INTEGER                                            :: handle, idomain, ndomains

      CALL timeset(routineN, handle)

      ndomains = SIZE(submatrices)
      DO idomain = 1, ndomains
         IF (submatrices(idomain)%domain .GT. 0) THEN
            CALL set_submatrix(submatrices(idomain), scalar)
         END IF
      END DO ! loop over domains

      CALL timestop(handle)

   END SUBROUTINE set_submatrix_array

! **************************************************************************************************
!> \brief ...
!> \param submatrix ...
!> \param scalar ...
! **************************************************************************************************
   SUBROUTINE set_submatrix(submatrix, scalar)

      TYPE(domain_submatrix_type), INTENT(INOUT)         :: submatrix
      REAL(KIND=dp), INTENT(IN)                          :: scalar

      CHARACTER(len=*), PARAMETER                        :: routineN = 'set_submatrix'

      INTEGER                                            :: ds1, ds2, handle, ms1, ms2

      CALL timeset(routineN, handle)

      CPASSERT(submatrix%domain .GT. 0)
      CPASSERT(submatrix%nrows .GT. 0)
      CPASSERT(submatrix%ncols .GT. 0)

      ds1 = submatrix%nrows
      ds2 = submatrix%ncols

      IF (.NOT. ALLOCATED(submatrix%mdata)) THEN
         ALLOCATE (submatrix%mdata(ds1, ds2))
      ELSE
         ms1 = SIZE(submatrix%mdata, 1)
         ms2 = SIZE(submatrix%mdata, 2)
         IF ((ds1 .NE. ms1) .OR. (ds2 .NE. ms2)) THEN
            DEALLOCATE (submatrix%mdata)
            ALLOCATE (submatrix%mdata(ds1, ds2))
         END IF
      END IF

      submatrix%mdata(:, :) = scalar

      CALL timestop(handle)

   END SUBROUTINE set_submatrix

! **************************************************************************************************
!> \brief ...
!> \param subm ...
! **************************************************************************************************
   SUBROUTINE release_submatrix_array(subm)

      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(INOUT)                                   :: subm

      CHARACTER(len=*), PARAMETER :: routineN = 'release_submatrix_array'

      INTEGER                                            :: handle, idomain, ndomains

      CALL timeset(routineN, handle)

      ndomains = SIZE(subm)
      DO idomain = 1, ndomains
         CALL release_submatrix(subm(idomain))
      END DO ! loop over domains

      CALL timestop(handle)

   END SUBROUTINE release_submatrix_array

! **************************************************************************************************
!> \brief ...
!> \param subm ...
! **************************************************************************************************
   SUBROUTINE release_submatrix(subm)

      TYPE(domain_submatrix_type), INTENT(INOUT)         :: subm

      CHARACTER(len=*), PARAMETER                        :: routineN = 'release_submatrix'

      INTEGER                                            :: handle

      CALL timeset(routineN, handle)

      subm%domain = -1
      subm%nbrows = -1
      subm%nbcols = -1
      subm%nrows = -1
      subm%ncols = -1
      subm%nnodes = -1
      subm%group = mp_comm_null

      IF (ALLOCATED(subm%dbcsr_row)) THEN
         DEALLOCATE (subm%dbcsr_row)
      END IF
      IF (ALLOCATED(subm%dbcsr_col)) THEN
         DEALLOCATE (subm%dbcsr_col)
      END IF
      IF (ALLOCATED(subm%size_brow)) THEN
         DEALLOCATE (subm%size_brow)
      END IF
      IF (ALLOCATED(subm%size_bcol)) THEN
         DEALLOCATE (subm%size_bcol)
      END IF
      IF (ALLOCATED(subm%mdata)) THEN
         DEALLOCATE (subm%mdata)
      END IF

      CALL timestop(handle)

   END SUBROUTINE release_submatrix

   ! more complex routine might be necessary if submatrices are distributed
! **************************************************************************************************
!> \brief ...
!> \param transA ...
!> \param transB ...
!> \param alpha ...
!> \param A ...
!> \param B ...
!> \param beta ...
!> \param C ...
! **************************************************************************************************
   SUBROUTINE multiply_submatrices_once(transA, transB, alpha, A, B, beta, C)

      CHARACTER, INTENT(IN)                              :: transA, transB
      REAL(KIND=dp), INTENT(IN)                          :: alpha
      TYPE(domain_submatrix_type), INTENT(IN)            :: A, B
      REAL(KIND=dp), INTENT(IN)                          :: beta
      TYPE(domain_submatrix_type), INTENT(INOUT)         :: C

      CHARACTER(len=*), PARAMETER :: routineN = 'multiply_submatrices_once'

      INTEGER                                            :: cs1, cs2, handle, icol, irow, K, K1, &
                                                            LDA, LDB, LDC, M, Mblocks, N, Nblocks
      LOGICAL                                            :: NOTA, NOTB

      CALL timeset(routineN, handle)

      CPASSERT(A%domain .GT. 0)
      CPASSERT(B%domain .GT. 0)
      CPASSERT(C%domain .GT. 0)

      LDA = SIZE(A%mdata, 1)
      LDB = SIZE(B%mdata, 1)

      NOTA = (transA .EQ. 'N') .OR. (transA .EQ. 'n')
      NOTB = (transB .EQ. 'N') .OR. (transB .EQ. 'n')

      IF (NOTA) THEN
         M = A%nrows
         K = A%ncols
         Mblocks = A%nbrows
      ELSE
         M = A%ncols
         K = A%nrows
         Mblocks = A%nbcols
      END IF

      IF (NOTB) THEN
         K1 = B%nrows
         N = B%ncols
         Nblocks = B%nbcols
      ELSE
         K1 = B%ncols
         N = B%nrows
         Nblocks = B%nbrows
      END IF

      ! these checks are for debugging only
      CPASSERT(K .EQ. K1)

      ! conform C matrix
      C%nrows = M
      C%ncols = N
      C%nbrows = Mblocks
      C%nbcols = Nblocks
      IF (ALLOCATED(C%dbcsr_row)) THEN
         DEALLOCATE (C%dbcsr_row)
      END IF
      ALLOCATE (C%dbcsr_row(C%nbrows))
      IF (ALLOCATED(C%dbcsr_col)) THEN
         DEALLOCATE (C%dbcsr_col)
      END IF
      ALLOCATE (C%dbcsr_col(C%nbcols))
      IF (ALLOCATED(C%size_brow)) THEN
         DEALLOCATE (C%size_brow)
      END IF
      ALLOCATE (C%size_brow(C%nbrows))
      IF (ALLOCATED(C%size_bcol)) THEN
         DEALLOCATE (C%size_bcol)
      END IF
      ALLOCATE (C%size_bcol(C%nbcols))

      DO irow = 1, C%nbrows
         IF (NOTA) THEN
            C%dbcsr_row(irow) = A%dbcsr_row(irow)
            C%size_brow(irow) = A%size_brow(irow)
         ELSE
            C%dbcsr_row(irow) = A%dbcsr_col(irow)
            C%size_brow(irow) = A%size_bcol(irow)
         END IF
      END DO

      DO icol = 1, C%nbcols
         IF (NOTB) THEN
            C%dbcsr_col(icol) = B%dbcsr_col(icol)
            C%size_bcol(icol) = B%size_bcol(icol)
         ELSE
            C%dbcsr_col(icol) = B%dbcsr_row(icol)
            C%size_bcol(icol) = B%size_brow(icol)
         END IF
      END DO

      IF (.NOT. ALLOCATED(C%mdata)) THEN
         !!! cannot use non-zero beta if C is not allocated
         CPASSERT(beta .EQ. 0.0_dp)
         ALLOCATE (C%mdata(C%nrows, C%ncols))
      ELSE
         cs1 = SIZE(C%mdata, 1)
         cs2 = SIZE(C%mdata, 2)
         IF ((C%nrows .NE. cs1) .OR. (C%ncols .NE. cs2)) THEN
            !!! cannot deallocate data if beta is non-zero
            CPASSERT(beta .EQ. 0.0_dp)
            DEALLOCATE (C%mdata)
            ALLOCATE (C%mdata(C%nrows, C%ncols))
         END IF
      END IF

      LDC = C%nrows

      CALL DGEMM(transA, transB, M, N, K, alpha, A%mdata, LDA, B%mdata, LDB, beta, C%mdata, LDC)

      C%nnodes = A%nnodes
      C%group = A%group

      CALL timestop(handle)

   END SUBROUTINE multiply_submatrices_once

! **************************************************************************************************
!> \brief ...
!> \param transA ...
!> \param transB ...
!> \param alpha ...
!> \param A ...
!> \param B ...
!> \param beta ...
!> \param C ...
! **************************************************************************************************
   SUBROUTINE multiply_submatrices_array(transA, transB, alpha, A, B, beta, C)

      CHARACTER, INTENT(IN)                              :: transA, transB
      REAL(KIND=dp), INTENT(IN)                          :: alpha
      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(IN)                                      :: A, B
      REAL(KIND=dp), INTENT(IN)                          :: beta
      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(INOUT)                                   :: C

      CHARACTER(len=*), PARAMETER :: routineN = 'multiply_submatrices_array'

      INTEGER                                            :: handle, idomain, idomainA, idomainB, &
                                                            ndomains, ndomainsB, ndomainsC

      CALL timeset(routineN, handle)

      ndomains = SIZE(A)
      ndomainsB = SIZE(B)
      ndomainsC = SIZE(C)

      CPASSERT(ndomains .EQ. ndomainsB)
      CPASSERT(ndomainsB .EQ. ndomainsC)

      DO idomain = 1, ndomains

         idomainA = A(idomain)%domain
         idomainB = B(idomain)%domain

         CPASSERT(idomainA .EQ. idomainB)

         C(idomain)%domain = idomainA

         ! check if the submatrix exists
         IF (idomainA .GT. 0) THEN
            CALL multiply_submatrices_once(transA, transB, alpha, A(idomain), B(idomain), beta, C(idomain))
         END IF ! submatrix for the domain exists

      END DO ! loop over domains

      CALL timestop(handle)

   END SUBROUTINE multiply_submatrices_array

   ! more complex routine might be necessary if submatrices are distributed
! **************************************************************************************************
!> \brief ...
!> \param alpha ...
!> \param A ...
!> \param beta ...
!> \param B ...
!> \param transB ...
! **************************************************************************************************
   SUBROUTINE add_submatrices_once(alpha, A, beta, B, transB)

      REAL(KIND=dp), INTENT(IN)                          :: alpha
      TYPE(domain_submatrix_type), INTENT(INOUT)         :: A
      REAL(KIND=dp), INTENT(IN)                          :: beta
      TYPE(domain_submatrix_type), INTENT(IN)            :: B
      CHARACTER, INTENT(IN)                              :: transB

      CHARACTER(len=*), PARAMETER :: routineN = 'add_submatrices_once'

      INTEGER                                            :: C1, C2, handle, icol, R1, R2
      LOGICAL                                            :: NOTB

      CALL timeset(routineN, handle)

      CPASSERT(A%domain .GT. 0)
      CPASSERT(B%domain .GT. 0)

      R1 = A%nrows
      C1 = A%ncols

      NOTB = (transB .EQ. 'N') .OR. (transB .EQ. 'n')

      IF (NOTB) THEN
         R2 = B%nrows
         C2 = B%ncols
      ELSE
         R2 = B%ncols
         C2 = B%nrows
      END IF

      ! these checks are for debugging only
      CPASSERT(C1 .EQ. C2)
      CPASSERT(R1 .EQ. R2)

      IF (NOTB) THEN
         DO icol = 1, C1
            A%mdata(:, icol) = alpha*A%mdata(:, icol) + beta*B%mdata(:, icol)
         END DO
      ELSE
         DO icol = 1, C1
            A%mdata(:, icol) = alpha*A%mdata(:, icol) + beta*B%mdata(icol, :)
         END DO
      END IF

      CALL timestop(handle)

   END SUBROUTINE add_submatrices_once

! **************************************************************************************************
!> \brief ...
!> \param alpha ...
!> \param A ...
!> \param beta ...
!> \param B ...
!> \param transB ...
! **************************************************************************************************
   SUBROUTINE add_submatrices_array(alpha, A, beta, B, transB)

      REAL(KIND=dp), INTENT(IN)                          :: alpha
      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(INOUT)                                   :: A
      REAL(KIND=dp), INTENT(IN)                          :: beta
      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(IN)                                      :: B
      CHARACTER, INTENT(IN)                              :: transB

      CHARACTER(len=*), PARAMETER :: routineN = 'add_submatrices_array'

      INTEGER                                            :: handle, idomain, idomainA, idomainB, &
                                                            ndomains, ndomainsB

      CALL timeset(routineN, handle)

      ndomains = SIZE(A)
      ndomainsB = SIZE(B)

      CPASSERT(ndomains .EQ. ndomainsB)

      DO idomain = 1, ndomains

         idomainA = A(idomain)%domain
         idomainB = B(idomain)%domain

         CPASSERT(idomainA .EQ. idomainB)

         ! check if the submatrix exists
         IF (idomainA .GT. 0) THEN
            CALL add_submatrices_once(alpha, A(idomain), beta, B(idomain), transB)
         END IF ! submatrix for the domain exists

      END DO ! loop over domains

      CALL timestop(handle)

   END SUBROUTINE add_submatrices_array

! **************************************************************************************************
!> \brief Computes the max norm of the collection of submatrices
!> \param submatrices ...
!> \param norm ...
!> \par History
!>       2013.03 created [Rustam Z. Khaliullin]
!> \author Rustam Z. Khaliullin
! **************************************************************************************************
   SUBROUTINE maxnorm_submatrices(submatrices, norm)

      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(IN)                                      :: submatrices
      REAL(KIND=dp), INTENT(OUT)                         :: norm

      CHARACTER(len=*), PARAMETER :: routineN = 'maxnorm_submatrices'

      INTEGER                                            :: handle, idomain, ndomains
      REAL(KIND=dp)                                      :: curr_norm, send_norm
      REAL(KIND=dp), ALLOCATABLE, DIMENSION(:)           :: recv_norm

      CALL timeset(routineN, handle)

      send_norm = 0.0_dp

      ndomains = SIZE(submatrices)

      DO idomain = 1, ndomains

         ! check if the submatrix is local
         IF (submatrices(idomain)%domain .GT. 0) THEN
            curr_norm = MAXVAL(ABS(submatrices(idomain)%mdata))
            IF (curr_norm .GT. send_norm) send_norm = curr_norm
         END IF

      END DO ! loop over domains

      ! communicate local norm to the other nodes
      ALLOCATE (recv_norm(submatrices(1)%nnodes))
      CALL submatrices(1)%group%allgather(send_norm, recv_norm)

      norm = MAXVAL(recv_norm)

      DEALLOCATE (recv_norm)

      CALL timestop(handle)

   END SUBROUTINE maxnorm_submatrices

! **************************************************************************************************
!> \brief Computes the sum of traces of the submatrix A.tr(B)
!> \param A ...
!> \param B ...
!> \param trace ...
!> \par History
!>       2013.03 created [Rustam Z. Khaliullin]
!> \author Rustam Z. Khaliullin
! **************************************************************************************************
   SUBROUTINE trace_submatrices(A, B, trace)

      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(IN)                                      :: A, B
      REAL(KIND=dp), INTENT(OUT)                         :: trace

      CHARACTER(len=*), PARAMETER                        :: routineN = 'trace_submatrices'

      INTEGER                                            :: domainA, domainB, handle, idomain, &
                                                            ndomainsA, ndomainsB
      REAL(KIND=dp)                                      :: curr_trace, send_trace
      REAL(KIND=dp), ALLOCATABLE, DIMENSION(:)           :: recv_trace

      CALL timeset(routineN, handle)

      send_trace = 0.0_dp

      ndomainsA = SIZE(A)
      ndomainsB = SIZE(B)

      CPASSERT(ndomainsA .EQ. ndomainsB)

      DO idomain = 1, ndomainsA

         domainA = A(idomain)%domain
         domainB = B(idomain)%domain

         CPASSERT(domainA .EQ. domainB)

         ! check if the submatrix is local
         IF (domainA .GT. 0) THEN

            CPASSERT(A(idomain)%nrows .EQ. B(idomain)%nrows)
            CPASSERT(A(idomain)%ncols .EQ. B(idomain)%ncols)

            curr_trace = SUM(A(idomain)%mdata(:, :)*B(idomain)%mdata(:, :))
            send_trace = send_trace + curr_trace

         END IF

      END DO ! loop over domains

      ! communicate local norm to the other nodes
      ALLOCATE (recv_trace(A(1)%nnodes))
      CALL A(1)%group%allgather(send_trace, recv_trace)

      trace = SUM(recv_trace)

      DEALLOCATE (recv_trace)

      CALL timestop(handle)

   END SUBROUTINE trace_submatrices

! **************************************************************************************************
!> \brief Constructs submatrices for each ALMO domain by collecting distributed
!>        DBCSR blocks to local arrays
!> \param matrix ...
!> \param submatrix ...
!> \param distr_pattern ...
!> \param domain_map ...
!> \param node_of_domain ...
!> \param job_type ...
!> \par History
!>       2013.01 created [Rustam Z. Khaliullin]
!> \author Rustam Z. Khaliullin
! **************************************************************************************************
   SUBROUTINE construct_submatrices(matrix, submatrix, distr_pattern, domain_map, &
                                    node_of_domain, job_type)

      TYPE(dbcsr_type), INTENT(IN)                       :: matrix
      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(INOUT)                                   :: submatrix
      TYPE(dbcsr_type), INTENT(IN)                       :: distr_pattern
      TYPE(domain_map_type), INTENT(IN)                  :: domain_map
      INTEGER, DIMENSION(:), INTENT(IN)                  :: node_of_domain
      INTEGER, INTENT(IN)                                :: job_type

      CHARACTER(len=*), PARAMETER :: routineN = 'construct_submatrices'

      CHARACTER                                          :: matrix_type
      INTEGER :: block_node, block_offset, col, col_offset, col_size, dest_node, GroupID, handle, &
         iBlock, icol, idomain, index_col, index_ec, index_er, index_row, index_sc, index_sr, &
         iNode, ldesc, myNode, nblkcols_tot, nblkrows_tot, ndomains, ndomains2, nNodes, &
         recv_size2_total, recv_size_total, row, row_size, send_size2_total, send_size_total, &
         smcol, smrow, start_data
      INTEGER, ALLOCATABLE, DIMENSION(:) :: first_col, first_row, offset2_block, offset_block, &
         recv_data2, recv_offset2_cpu, recv_offset_cpu, recv_size2_cpu, recv_size_cpu, send_data2, &
         send_offset2_cpu, send_offset_cpu, send_size2_cpu, send_size_cpu
      INTEGER, ALLOCATABLE, DIMENSION(:, :)              :: recv_descriptor, send_descriptor
      INTEGER, DIMENSION(:), POINTER                     :: col_blk_size, row_blk_size
      LOGICAL                                            :: found, transp
      REAL(KIND=dp)                                      :: antifactor
      REAL(KIND=dp), ALLOCATABLE, DIMENSION(:)           :: recv_data, send_data
      REAL(KIND=dp), DIMENSION(:), POINTER               :: block_p
      TYPE(dbcsr_distribution_type)                      :: pattern_dist
      TYPE(mp_comm_type)                                 :: group

!INTEGER, PARAMETER                         :: select_row_col = 1
!INTEGER, PARAMETER                         :: select_row = 2
!                                                  subm_row_size,&
!                                                  subm_col_size,&

      CALL timeset(routineN, handle)

      nblkrows_tot = dbcsr_nblkrows_total(matrix)
      nblkcols_tot = dbcsr_nblkcols_total(matrix)

      ndomains = nblkcols_tot ! RZK-warning not true for atomic distributions
      CALL dbcsr_get_info(distr_pattern, distribution=pattern_dist)
      CALL dbcsr_distribution_get(pattern_dist, numnodes=nNodes, group=GroupID, mynode=myNode)

      CALL group%set_handle(groupid)

      matrix_type = dbcsr_get_matrix_type(matrix)

      ldesc = 2
      ALLOCATE (send_descriptor(ldesc, nNodes))
      ALLOCATE (recv_descriptor(ldesc, nNodes))
      send_descriptor(:, :) = 0

      ! find: the number of blocks and their sizes that must be sent to each cpu
      ! loop over all domains
      DO idomain = 1, ndomains

         dest_node = node_of_domain(idomain)

         ! loop over those rows that have non-zero quencher
         index_sr = 1 ! index start row
         IF (idomain .GT. 1) index_sr = domain_map%index1(idomain - 1)
         index_er = domain_map%index1(idomain) - 1 ! index end row

         DO index_row = index_sr, index_er

            row = domain_map%pairs(index_row, 1)

            IF (job_type == select_row_col) THEN
               ! loop over those columns that have non-zero quencher
               index_sc = 1 ! index start col
               IF (idomain .GT. 1) index_sc = domain_map%index1(idomain - 1)
               index_ec = domain_map%index1(idomain) - 1 ! index end col
            ELSE
               ! fake loop
               index_sc = 1 ! index start col
               index_ec = 1 ! index end col
            END IF

            DO index_col = index_sc, index_ec

               IF (job_type == select_row_col) THEN
                  col = domain_map%pairs(index_col, 1)
               ELSE
                  col = idomain
               END IF

               transp = .FALSE.
               CALL dbcsr_get_stored_coordinates(matrix, &
                                                 row, col, block_node)
               IF (block_node .EQ. myNode) THEN
                  CALL dbcsr_get_block_p(matrix, row, col, block_p, found, row_size, col_size)
                  IF (found) THEN
                     send_descriptor(1, dest_node + 1) = send_descriptor(1, dest_node + 1) + 1
                     send_descriptor(2, dest_node + 1) = send_descriptor(2, dest_node + 1) + &
                                                         row_size*col_size
                  END IF
               END IF

            END DO ! loop over columns

         END DO ! loop over rows

      END DO

      ! simple but quadratically scaling procedure
      ! loop over local blocks
      !CALL dbcsr_iterator_start(iter,matrix)
      !DO WHILE (dbcsr_iterator_blocks_left(iter))
      !   CALL dbcsr_iterator_next_block(iter,row,col,data_p,&
      !           row_size=row_size,col_size=col_size)
      !   DO idomain = 1, ndomains
      !      IF (job_type==select_row_col) THEN
      !         domain_needs_block=(qblk_exists(domain_map,col,idomain)&
      !            .AND.qblk_exists(domain_map,row,idomain))
      !      ELSE
      !         domain_needs_block=(idomain==col&
      !            .AND.qblk_exists(domain_map,row,idomain))
      !      ENDIF
      !      IF (domain_needs_block) THEN
      !         transp=.FALSE.
      !         dest_node=node_of_domain(idomain)
      !         !CALL dbcsr_get_stored_coordinates(distr_pattern,&
      !         !        idomain, idomain, transp, dest_node)
      !         send_descriptor(1,dest_node+1)=send_descriptor(1,dest_node+1)+1
      !         send_descriptor(2,dest_node+1)=send_descriptor(2,dest_node+1)+&
      !            row_size*col_size
      !      ENDIF
      !   ENDDO
      !ENDDO
      !CALL dbcsr_iterator_stop(iter)

      ! communicate number of blocks and their sizes to the other nodes
      CALL group%alltoall(send_descriptor, recv_descriptor, ldesc)

      ALLOCATE (send_size_cpu(nNodes), send_offset_cpu(nNodes))
      send_offset_cpu(1) = 0
      send_size_cpu(1) = send_descriptor(2, 1)
      DO iNode = 2, nNodes
         send_size_cpu(iNode) = send_descriptor(2, iNode)
         send_offset_cpu(iNode) = send_offset_cpu(iNode - 1) + &
                                  send_size_cpu(iNode - 1)
      END DO
      send_size_total = send_offset_cpu(nNodes) + send_size_cpu(nNodes)

      ALLOCATE (recv_size_cpu(nNodes), recv_offset_cpu(nNodes))
      recv_offset_cpu(1) = 0
      recv_size_cpu(1) = recv_descriptor(2, 1)
      DO iNode = 2, nNodes
         recv_size_cpu(iNode) = recv_descriptor(2, iNode)
         recv_offset_cpu(iNode) = recv_offset_cpu(iNode - 1) + &
                                  recv_size_cpu(iNode - 1)
      END DO
      recv_size_total = recv_offset_cpu(nNodes) + recv_size_cpu(nNodes)

      ALLOCATE (send_size2_cpu(nNodes), send_offset2_cpu(nNodes))
      send_offset2_cpu(1) = 0
      send_size2_cpu(1) = 2*send_descriptor(1, 1)
      DO iNode = 2, nNodes
         send_size2_cpu(iNode) = 2*send_descriptor(1, iNode)
         send_offset2_cpu(iNode) = send_offset2_cpu(iNode - 1) + &
                                   send_size2_cpu(iNode - 1)
      END DO
      send_size2_total = send_offset2_cpu(nNodes) + send_size2_cpu(nNodes)

      ALLOCATE (recv_size2_cpu(nNodes), recv_offset2_cpu(nNodes))
      recv_offset2_cpu(1) = 0
      recv_size2_cpu(1) = 2*recv_descriptor(1, 1)
      DO iNode = 2, nNodes
         recv_size2_cpu(iNode) = 2*recv_descriptor(1, iNode)
         recv_offset2_cpu(iNode) = recv_offset2_cpu(iNode - 1) + &
                                   recv_size2_cpu(iNode - 1)
      END DO
      recv_size2_total = recv_offset2_cpu(nNodes) + recv_size2_cpu(nNodes)

      DEALLOCATE (send_descriptor)
      DEALLOCATE (recv_descriptor)

      ! collect data from the matrix into send_data
      ALLOCATE (send_data(send_size_total))
      ALLOCATE (recv_data(recv_size_total))
      ALLOCATE (send_data2(send_size2_total))
      ALLOCATE (recv_data2(recv_size2_total))
      ALLOCATE (offset_block(nNodes))
      ALLOCATE (offset2_block(nNodes))
      offset_block(:) = 0
      offset2_block(:) = 0
      ! loop over all domains
      DO idomain = 1, ndomains

         dest_node = node_of_domain(idomain)

         ! loop over those rows that have non-zero quencher
         index_sr = 1 ! index start row
         IF (idomain .GT. 1) index_sr = domain_map%index1(idomain - 1)
         index_er = domain_map%index1(idomain) - 1 ! index end row

         DO index_row = index_sr, index_er

            row = domain_map%pairs(index_row, 1)

            IF (job_type == select_row_col) THEN
               ! loop over those columns that have non-zero quencher
               index_sc = 1 ! index start col
               IF (idomain .GT. 1) index_sc = domain_map%index1(idomain - 1)
               index_ec = domain_map%index1(idomain) - 1 ! index end col
            ELSE
               ! fake loop
               index_sc = 1 ! index start col
               index_ec = 1 ! index end col
            END IF

            DO index_col = index_sc, index_ec

               IF (job_type == select_row_col) THEN
                  col = domain_map%pairs(index_col, 1)
               ELSE
                  col = idomain
               END IF

               transp = .FALSE.
               CALL dbcsr_get_stored_coordinates(matrix, &
                                                 row, col, block_node)
               IF (block_node .EQ. myNode) THEN
                  CALL dbcsr_get_block_p(matrix, row, col, block_p, found, row_size, col_size)
                  IF (found) THEN
                     !col_offset=0
                     !DO icol=1,col_size
                     !   start_data=send_offset_cpu(dest_node+1)+&
                     !              offset_block(dest_node+1)+&
                     !              col_offset
                     !   send_data(start_data+1:start_data+row_size)=&
                     !      data_p(1:row_size,icol)
                     !   col_offset=col_offset+row_size
                     !ENDDO
                     col_offset = row_size*col_size
                     start_data = send_offset_cpu(dest_node + 1) + &
                                  offset_block(dest_node + 1)
                     send_data(start_data + 1:start_data + col_offset) = &
                        block_p(1:col_offset)
                     offset_block(dest_node + 1) = offset_block(dest_node + 1) + col_offset
                     ! fill out row,col information
                     send_data2(send_offset2_cpu(dest_node + 1) + &
                                offset2_block(dest_node + 1) + 1) = row
                     send_data2(send_offset2_cpu(dest_node + 1) + &
                                offset2_block(dest_node + 1) + 2) = col
                     offset2_block(dest_node + 1) = offset2_block(dest_node + 1) + 2
                  END IF
               END IF

            END DO ! loop over columns

         END DO ! loop over rows

      END DO
      ! more simple but quadratically scaling version
      !CALL dbcsr_iterator_start(iter,matrix)
      !DO WHILE (dbcsr_iterator_blocks_left(iter))
      !   CALL dbcsr_iterator_next_block(iter,row,col,data_p,&
      !           row_size=row_size,col_size=col_size)
      !   DO idomain = 1, ndomains
      !      IF (job_type==select_row_col) THEN
      !         domain_needs_block=(qblk_exists(domain_map,col,idomain)&
      !            .AND.qblk_exists(domain_map,row,idomain))
      !      ELSE
      !         domain_needs_block=(idomain==col&
      !            .AND.qblk_exists(domain_map,row,idomain))
      !      ENDIF
      !      IF (domain_needs_block) THEN
      !         transp=.FALSE.
      !         dest_node=node_of_domain(idomain)
      !         !CALL dbcsr_get_stored_coordinates(distr_pattern,&
      !         !        idomain, idomain, transp, dest_node)
      !         ! place the data appropriately
      !         col_offset=0
      !         DO icol=1,col_size
      !            start_data=send_offset_cpu(dest_node+1)+&
      !                       offset_block(dest_node+1)+&
      !                       col_offset
      !            send_data(start_data+1:start_data+row_size)=&
      !               data_p(1:row_size,icol)
      !            col_offset=col_offset+row_size
      !         ENDDO
      !         offset_block(dest_node+1)=offset_block(dest_node+1)+col_size*row_size
      !         ! fill out row,col information
      !         send_data2(send_offset2_cpu(dest_node+1)+&
      !               offset2_block(dest_node+1)+1)=row
      !         send_data2(send_offset2_cpu(dest_node+1)+&
      !               offset2_block(dest_node+1)+2)=col
      !         offset2_block(dest_node+1)=offset2_block(dest_node+1)+2
      !      ENDIF
      !   ENDDO
      !ENDDO
      !CALL dbcsr_iterator_stop(iter)

      ! send-receive all blocks
      CALL group%alltoall(send_data, send_size_cpu, send_offset_cpu, &
                          recv_data, recv_size_cpu, recv_offset_cpu)
      ! send-receive rows and cols of the blocks
      CALL group%alltoall(send_data2, send_size2_cpu, send_offset2_cpu, &
                          recv_data2, recv_size2_cpu, recv_offset2_cpu)

      DEALLOCATE (send_size_cpu, send_offset_cpu)
      DEALLOCATE (send_size2_cpu, send_offset2_cpu)
      DEALLOCATE (send_data)
      DEALLOCATE (send_data2)
      DEALLOCATE (offset_block)
      DEALLOCATE (offset2_block)

      ! copy blocks into submatrices
      CALL dbcsr_get_info(matrix, col_blk_size=col_blk_size, row_blk_size=row_blk_size)
!    ALLOCATE(subm_row_size(ndomains),subm_col_size(ndomains))
!    subm_row_size(:)=0
!    subm_col_size(:)=0
      ndomains2 = SIZE(submatrix)
      IF (ndomains2 .NE. ndomains) THEN
         CPABORT("wrong submatrix size")
      END IF
      CALL release_submatrices(submatrix)
      submatrix(:)%nnodes = nNodes
      submatrix(:)%group = Group
      submatrix(:)%nrows = 0
      submatrix(:)%ncols = 0

      ALLOCATE (first_row(nblkrows_tot), first_col(nblkcols_tot))
      submatrix(:)%domain = -1
      DO idomain = 1, ndomains
         dest_node = node_of_domain(idomain)
         !transp=.FALSE.
         !CALL dbcsr_get_stored_coordinates(distr_pattern,&
         !        idomain, idomain, transp, dest_node)
         IF (dest_node .EQ. mynode) THEN
            submatrix(idomain)%domain = idomain
            submatrix(idomain)%nbrows = 0
            submatrix(idomain)%nbcols = 0

            ! loop over those rows that have non-zero quencher
            first_row(:) = -1
            index_sr = 1 ! index start row
            IF (idomain .GT. 1) index_sr = domain_map%index1(idomain - 1)
            index_er = domain_map%index1(idomain) - 1 ! index end row
            DO index_row = index_sr, index_er
               row = domain_map%pairs(index_row, 1)
               !DO row = 1, nblkrows_tot
               !   IF (qblk_exists(domain_map,row,idomain)) THEN
               first_row(row) = submatrix(idomain)%nrows + 1
               submatrix(idomain)%nrows = submatrix(idomain)%nrows + row_blk_size(row)
               submatrix(idomain)%nbrows = submatrix(idomain)%nbrows + 1
               !   ENDIF
            END DO
            ALLOCATE (submatrix(idomain)%dbcsr_row(submatrix(idomain)%nbrows))
            ALLOCATE (submatrix(idomain)%size_brow(submatrix(idomain)%nbrows))
            smrow = 1
            ! again loop over those rows that have non-zero quencher
            index_sr = 1 ! index start row
            IF (idomain .GT. 1) index_sr = domain_map%index1(idomain - 1)
            index_er = domain_map%index1(idomain) - 1 ! index end row
            DO index_row = index_sr, index_er
               row = domain_map%pairs(index_row, 1)
               !DO row = 1, nblkrows_tot
               !   IF (first_row(row).ne.-1) THEN
               submatrix(idomain)%dbcsr_row(smrow) = row
               submatrix(idomain)%size_brow(smrow) = row_blk_size(row)
               smrow = smrow + 1
               !   ENDIF
            END DO

            ! loop over the necessary columns
            first_col(:) = -1
            IF (job_type == select_row_col) THEN
               ! loop over those columns that have non-zero quencher
               index_sc = 1 ! index start col
               IF (idomain .GT. 1) index_sc = domain_map%index1(idomain - 1)
               index_ec = domain_map%index1(idomain) - 1 ! index end col
            ELSE
               ! fake loop
               index_sc = 1 ! index start col
               index_ec = 1 ! index end col
            END IF
            DO index_col = index_sc, index_ec
               IF (job_type == select_row_col) THEN
                  col = domain_map%pairs(index_col, 1)
               ELSE
                  col = idomain
               END IF
               !DO col = 1, nblkcols_tot
               !   IF (job_type==select_row_col) THEN
               !      domain_needs_block=(qblk_exists(domain_map,col,idomain))
               !   ELSE
               !      domain_needs_block=(col==idomain) ! RZK-warning col belongs to the domain
               !   ENDIF
               !   IF (domain_needs_block) THEN
               first_col(col) = submatrix(idomain)%ncols + 1
               submatrix(idomain)%ncols = submatrix(idomain)%ncols + col_blk_size(col)
               submatrix(idomain)%nbcols = submatrix(idomain)%nbcols + 1
               !   ENDIF
            END DO

            ALLOCATE (submatrix(idomain)%dbcsr_col(submatrix(idomain)%nbcols))
            ALLOCATE (submatrix(idomain)%size_bcol(submatrix(idomain)%nbcols))

            ! loop over the necessary columns again
            smcol = 1
            IF (job_type == select_row_col) THEN
               ! loop over those columns that have non-zero quencher
               index_sc = 1 ! index start col
               IF (idomain .GT. 1) index_sc = domain_map%index1(idomain - 1)
               index_ec = domain_map%index1(idomain) - 1 ! index end col
            ELSE
               ! fake loop
               index_sc = 1 ! index start col
               index_ec = 1 ! index end col
            END IF
            DO index_col = index_sc, index_ec
               IF (job_type == select_row_col) THEN
                  col = domain_map%pairs(index_col, 1)
               ELSE
                  col = idomain
               END IF
               !DO col = 1, nblkcols_tot
               !   IF (first_col(col).ne.-1) THEN
               submatrix(idomain)%dbcsr_col(smcol) = col
               submatrix(idomain)%size_bcol(smcol) = col_blk_size(col)
               smcol = smcol + 1
               !   ENDIF
            END DO

            ALLOCATE (submatrix(idomain)%mdata( &
                      submatrix(idomain)%nrows, &
                      submatrix(idomain)%ncols))
            submatrix(idomain)%mdata(:, :) = 0.0_dp
            DO iNode = 1, nNodes
               block_offset = 0
               DO iBlock = 1, recv_size2_cpu(iNode)/2
                  ! read the (row,col) of the block
                  row = recv_data2(recv_offset2_cpu(iNode) + (iBlock - 1)*2 + 1)
                  col = recv_data2(recv_offset2_cpu(iNode) + (iBlock - 1)*2 + 2)
                  ! check if this block should be in the submatrix of this domain
                  IF ((first_col(col) .NE. -1) .AND. (first_row(row) .NE. -1)) THEN
                     ! copy data from the received array into submatrix
                     start_data = recv_offset_cpu(iNode) + block_offset + 1
                     DO icol = 0, col_blk_size(col) - 1
                        submatrix(idomain)%mdata(first_row(row): &
                                                 first_row(row) + row_blk_size(row) - 1, &
                                                 first_col(col) + icol) = &
                           recv_data(start_data:start_data + row_blk_size(row) - 1)
                        start_data = start_data + row_blk_size(row)
                     END DO
                     IF (job_type == select_row_col) THEN
                        IF (matrix_type == dbcsr_type_symmetric .OR. &
                            matrix_type == dbcsr_type_antisymmetric) THEN
                           ! copy data into the transposed block as well
                           antifactor = 1.0_dp
                           IF (matrix_type == dbcsr_type_antisymmetric) THEN
                              antifactor = -1.0_dp
                           END IF
                           start_data = recv_offset_cpu(iNode) + block_offset + 1
                           DO icol = 0, col_blk_size(col) - 1
                              submatrix(idomain)%mdata(first_row(col) + icol, &
                                                       first_col(row): &
                                                       first_col(row) + row_blk_size(row) - 1) = &
                                 antifactor*recv_data(start_data: &
                                                      start_data + row_blk_size(row) - 1)
                              start_data = start_data + row_blk_size(row)
                           END DO
                        ELSE IF (matrix_type == dbcsr_type_no_symmetry) THEN
                        ELSE
                           CPABORT("matrix type is NYI")
                        END IF
                     END IF
                  END IF
                  block_offset = block_offset + col_blk_size(col)*row_blk_size(row)
               END DO
            END DO
         END IF ! mynode.eq.dest_node
      END DO ! loop over domains

      DEALLOCATE (recv_size_cpu, recv_offset_cpu)
      DEALLOCATE (recv_size2_cpu, recv_offset2_cpu)
      DEALLOCATE (recv_data)
      DEALLOCATE (recv_data2)
!    DEALLOCATE(subm_row_size,subm_col_size)
      DEALLOCATE (first_row, first_col)

      CALL timestop(handle)

   END SUBROUTINE construct_submatrices

! **************************************************************************************************
!> \brief Constructs a DBCSR matrix from submatrices
!> \param matrix ...
!> \param submatrix ...
!> \param distr_pattern ...
!> \par History
!>       2013.01 created [Rustam Z. Khaliullin]
!> \author Rustam Z. Khaliullin
! **************************************************************************************************
   SUBROUTINE construct_dbcsr_from_submatrices(matrix, submatrix, distr_pattern)

      TYPE(dbcsr_type), INTENT(INOUT)                    :: matrix
      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(IN)                                      :: submatrix
      TYPE(dbcsr_type), INTENT(IN)                       :: distr_pattern

      CHARACTER(len=*), PARAMETER :: routineN = 'construct_dbcsr_from_submatrices'

      CHARACTER                                          :: matrix_type
      INTEGER :: block_offset, col, col_offset, colsize, dest_node, GroupID, handle, iBlock, icol, &
         idomain, iNode, irow_subm, ldesc, myNode, nblkcols_tot, nblkrows_tot, ndomains, &
         ndomains2, nNodes, recv_size2_total, recv_size_total, row, rowsize, send_size2_total, &
         send_size_total, smroff, start_data, unit_nr
      INTEGER, ALLOCATABLE, DIMENSION(:) :: offset2_block, offset_block, recv_data2, &
         recv_offset2_cpu, recv_offset_cpu, recv_size2_cpu, recv_size_cpu, send_data2, &
         send_offset2_cpu, send_offset_cpu, send_size2_cpu, send_size_cpu
      INTEGER, ALLOCATABLE, DIMENSION(:, :)              :: recv_descriptor, send_descriptor
      INTEGER, DIMENSION(:), POINTER                     :: col_blk_size, row_blk_size
      LOGICAL                                            :: transp
      REAL(KIND=dp), ALLOCATABLE, DIMENSION(:)           :: recv_data, send_data
      REAL(KIND=dp), DIMENSION(:, :), POINTER            :: block_p
      TYPE(cp_logger_type), POINTER                      :: logger
      TYPE(dbcsr_distribution_type)                      :: pattern_dist
      TYPE(dbcsr_iterator_type)                          :: iter
      TYPE(mp_comm_type)                                 :: group

      CALL timeset(routineN, handle)

      ! get a useful output_unit
      logger => cp_get_default_logger()
      IF (logger%para_env%is_source()) THEN
         unit_nr = cp_logger_get_default_unit_nr(logger, local=.TRUE.)
      ELSE
         unit_nr = -1
      END IF

      nblkrows_tot = dbcsr_nblkrows_total(matrix)
      nblkcols_tot = dbcsr_nblkcols_total(matrix)

      ndomains = nblkcols_tot ! RZK-warning not true for atomic distributions
      ndomains2 = SIZE(submatrix)

      IF (ndomains .NE. ndomains2) THEN
         CPABORT("domain mismatch")
      END IF

      CALL dbcsr_get_info(distr_pattern, distribution=pattern_dist)
      CALL dbcsr_distribution_get(pattern_dist, numnodes=nNodes, group=GroupID, mynode=myNode)

      CALL group%set_handle(GroupID)

      matrix_type = dbcsr_get_matrix_type(matrix)
      IF (matrix_type .NE. dbcsr_type_no_symmetry) THEN
         CPABORT("only non-symmetric matrices so far")
      END IF

      ! remove all blocks from the dbcsr matrix
      CALL dbcsr_iterator_start(iter, matrix)
      DO WHILE (dbcsr_iterator_blocks_left(iter))
         CALL dbcsr_iterator_next_block(iter, row, col, block_p)
         block_p(:, :) = 0.0_dp
      END DO
      CALL dbcsr_iterator_stop(iter)
      CALL dbcsr_filter(matrix, 0.1_dp)

      CALL dbcsr_work_create(matrix, work_mutable=.TRUE.)

      ldesc = 2
      ALLOCATE (send_descriptor(ldesc, nNodes))
      ALLOCATE (recv_descriptor(ldesc, nNodes))
      send_descriptor(:, :) = 0

      ! loop over domains - find how much data to send
      DO idomain = 1, ndomains

         IF (submatrix(idomain)%domain .GT. 0) THEN

            DO irow_subm = 1, submatrix(idomain)%nbrows

               IF (submatrix(idomain)%nbcols .NE. 1) THEN
                  CPABORT("corrupt submatrix structure")
               END IF

               row = submatrix(idomain)%dbcsr_row(irow_subm)
               col = submatrix(idomain)%dbcsr_col(1)

               IF (col .NE. idomain) THEN
                  CPABORT("corrupt submatrix structure")
               END IF

               transp = .FALSE.
               CALL dbcsr_get_stored_coordinates(distr_pattern, &
                                                 row, idomain, dest_node)

               send_descriptor(1, dest_node + 1) = send_descriptor(1, dest_node + 1) + 1
               send_descriptor(2, dest_node + 1) = send_descriptor(2, dest_node + 1) + &
                                                   submatrix(idomain)%size_brow(irow_subm)* &
                                                   submatrix(idomain)%size_bcol(1)

            END DO ! loop over submatrix blocks

         END IF

      END DO ! loop over domains

      ! communicate number of blocks and their sizes to the other nodes
      CALL group%alltoall(send_descriptor, recv_descriptor, ldesc)

      ALLOCATE (send_size_cpu(nNodes), send_offset_cpu(nNodes))
      send_offset_cpu(1) = 0
      send_size_cpu(1) = send_descriptor(2, 1)
      DO iNode = 2, nNodes
         send_size_cpu(iNode) = send_descriptor(2, iNode)
         send_offset_cpu(iNode) = send_offset_cpu(iNode - 1) + &
                                  send_size_cpu(iNode - 1)
      END DO
      send_size_total = send_offset_cpu(nNodes) + send_size_cpu(nNodes)

      ALLOCATE (recv_size_cpu(nNodes), recv_offset_cpu(nNodes))
      recv_offset_cpu(1) = 0
      recv_size_cpu(1) = recv_descriptor(2, 1)
      DO iNode = 2, nNodes
         recv_size_cpu(iNode) = recv_descriptor(2, iNode)
         recv_offset_cpu(iNode) = recv_offset_cpu(iNode - 1) + &
                                  recv_size_cpu(iNode - 1)
      END DO
      recv_size_total = recv_offset_cpu(nNodes) + recv_size_cpu(nNodes)

      ALLOCATE (send_size2_cpu(nNodes), send_offset2_cpu(nNodes))
      send_offset2_cpu(1) = 0
      send_size2_cpu(1) = 2*send_descriptor(1, 1)
      DO iNode = 2, nNodes
         send_size2_cpu(iNode) = 2*send_descriptor(1, iNode)
         send_offset2_cpu(iNode) = send_offset2_cpu(iNode - 1) + &
                                   send_size2_cpu(iNode - 1)
      END DO
      send_size2_total = send_offset2_cpu(nNodes) + send_size2_cpu(nNodes)

      ALLOCATE (recv_size2_cpu(nNodes), recv_offset2_cpu(nNodes))
      recv_offset2_cpu(1) = 0
      recv_size2_cpu(1) = 2*recv_descriptor(1, 1)
      DO iNode = 2, nNodes
         recv_size2_cpu(iNode) = 2*recv_descriptor(1, iNode)
         recv_offset2_cpu(iNode) = recv_offset2_cpu(iNode - 1) + &
                                   recv_size2_cpu(iNode - 1)
      END DO
      recv_size2_total = recv_offset2_cpu(nNodes) + recv_size2_cpu(nNodes)

      DEALLOCATE (send_descriptor)
      DEALLOCATE (recv_descriptor)

      ! collect data from the matrix into send_data
      ALLOCATE (send_data(send_size_total))
      ALLOCATE (recv_data(recv_size_total))
      ALLOCATE (send_data2(send_size2_total))
      ALLOCATE (recv_data2(recv_size2_total))
      ALLOCATE (offset_block(nNodes))
      ALLOCATE (offset2_block(nNodes))
      offset_block(:) = 0
      offset2_block(:) = 0
      ! loop over domains - collect data to send
      DO idomain = 1, ndomains

         IF (submatrix(idomain)%domain .GT. 0) THEN

            smroff = 0
            DO irow_subm = 1, submatrix(idomain)%nbrows

               row = submatrix(idomain)%dbcsr_row(irow_subm)
               col = submatrix(idomain)%dbcsr_col(1)

               rowsize = submatrix(idomain)%size_brow(irow_subm)
               colsize = submatrix(idomain)%size_bcol(1)

               transp = .FALSE.
               CALL dbcsr_get_stored_coordinates(distr_pattern, &
                                                 row, idomain, dest_node)

               ! place the data appropriately
               col_offset = 0
               DO icol = 1, colsize
                  start_data = send_offset_cpu(dest_node + 1) + &
                               offset_block(dest_node + 1) + &
                               col_offset
                  send_data(start_data + 1:start_data + rowsize) = &
                     submatrix(idomain)%mdata(smroff + 1:smroff + rowsize, icol)
                  col_offset = col_offset + rowsize
               END DO
               offset_block(dest_node + 1) = offset_block(dest_node + 1) + &
                                             colsize*rowsize
               ! fill out row,col information
               send_data2(send_offset2_cpu(dest_node + 1) + &
                          offset2_block(dest_node + 1) + 1) = row
               send_data2(send_offset2_cpu(dest_node + 1) + &
                          offset2_block(dest_node + 1) + 2) = col
               offset2_block(dest_node + 1) = offset2_block(dest_node + 1) + 2

               smroff = smroff + rowsize

            END DO

         END IF

      END DO ! loop over domains

      ! send-receive all blocks
      CALL group%alltoall(send_data, send_size_cpu, send_offset_cpu, &
                          recv_data, recv_size_cpu, recv_offset_cpu)
      ! send-receive rows and cols of the blocks
      CALL group%alltoall(send_data2, send_size2_cpu, send_offset2_cpu, &
                          recv_data2, recv_size2_cpu, recv_offset2_cpu)

      DEALLOCATE (send_size_cpu, send_offset_cpu)
      DEALLOCATE (send_size2_cpu, send_offset2_cpu)
      DEALLOCATE (send_data)
      DEALLOCATE (send_data2)
      DEALLOCATE (offset_block)
      DEALLOCATE (offset2_block)

      ! copy received data into dbcsr matrix
      CALL dbcsr_get_info(matrix, col_blk_size=col_blk_size, row_blk_size=row_blk_size)
      DO iNode = 1, nNodes
         block_offset = 0
         DO iBlock = 1, recv_size2_cpu(iNode)/2
            ! read the (row,col) of the block
            row = recv_data2(recv_offset2_cpu(iNode) + (iBlock - 1)*2 + 1)
            col = recv_data2(recv_offset2_cpu(iNode) + (iBlock - 1)*2 + 2)
            !CALL dbcsr_get_block_p(matrix,row,col,block_p,found)
            !IF (.NOT.found) THEN
            NULLIFY (block_p)
            CALL dbcsr_reserve_block2d(matrix, row, col, block_p)
            CPASSERT(ASSOCIATED(block_p))
            !ENDIF
            ! copy data from the received array into the matrix block
            start_data = recv_offset_cpu(iNode) + block_offset + 1
            DO icol = 1, col_blk_size(col)
               block_p(:, icol) = &
                  recv_data(start_data:start_data + row_blk_size(row) - 1)
               start_data = start_data + row_blk_size(row)
            END DO
            block_offset = block_offset + col_blk_size(col)*row_blk_size(row)
         END DO
      END DO

      DEALLOCATE (recv_size_cpu, recv_offset_cpu)
      DEALLOCATE (recv_size2_cpu, recv_offset2_cpu)
      DEALLOCATE (recv_data)
      DEALLOCATE (recv_data2)

      CALL dbcsr_finalize(matrix)

      CALL timestop(handle)

   END SUBROUTINE construct_dbcsr_from_submatrices

! **************************************************************************************************
!> \brief ...
!> \param submatrices ...
!> \param mpgroup ...
! **************************************************************************************************
   SUBROUTINE print_submatrices(submatrices, mpgroup)

      TYPE(domain_submatrix_type), DIMENSION(:), &
         INTENT(IN)                                      :: submatrices
      TYPE(mp_comm_type), INTENT(IN)                     :: mpgroup

      CHARACTER(len=*), PARAMETER                        :: routineN = 'print_submatrices'

      CHARACTER(len=30)                                  :: colstr, formatstr
      INTEGER                                            :: handle, i, irow, n, ncols, nrows

      CALL timeset(routineN, handle)

      n = SIZE(submatrices)

      DO i = 1, n
         nrows = SIZE(submatrices(i)%mdata, 1)
         ncols = SIZE(submatrices(i)%mdata, 2)
         WRITE (colstr, *) ncols
         formatstr = '('//TRIM(ADJUSTL(colstr))//'F16.9)'
         IF (submatrices(i)%domain .GT. 0) THEN
            WRITE (*, *) "SUBMATRIX: ", i, nrows, 'x', ncols
            nrows = SIZE(submatrices(i)%mdata, 1)
            DO irow = 1, nrows
               WRITE (*, formatstr) submatrices(i)%mdata(irow, :)
            END DO
         END IF
         CALL mpgroup%sync()
      END DO

      CALL timestop(handle)

   END SUBROUTINE print_submatrices

! **************************************************************************************************
!> \brief Reports whether the DBCSR block (row,col) exists in the quencher
!> \param map ...
!> \param row ...
!> \param col ...
!> \return ...
!> \par History
!>       2013.01 created [Rustam Z. Khaliullin]
!> \author Rustam Z. Khaliullin
! **************************************************************************************************
   FUNCTION qblk_exists(map, row, col)

      TYPE(domain_map_type), INTENT(IN)                  :: map
      INTEGER, INTENT(IN)                                :: row, col
      LOGICAL                                            :: qblk_exists

      INTEGER                                            :: first, last, mid, ndomains

!CALL timeset(routineN,handle)

      ndomains = SIZE(map%index1)

      qblk_exists = .FALSE.
      IF (col .LT. 1 .OR. col .GT. ndomains) RETURN
      first = 1
      IF (col .GT. 1) first = map%index1(col - 1)
      last = map%index1(col) - 1

      ! perform binary search within first-last
      DO WHILE (last .GE. first)
         mid = first + (last - first)/2
         IF (map%pairs(mid, 1) .GT. row) THEN
            last = mid - 1
         ELSE IF (map%pairs(mid, 1) .LT. row) THEN
            first = mid + 1
         ELSE
            qblk_exists = .TRUE. ! SUCCESS!!
            EXIT
         END IF
      END DO

      !CALL timestop(handle)

      RETURN

   END FUNCTION qblk_exists

END MODULE domain_submatrix_methods

