amg4psblas/mlprec/mld_sslud_bld.f90

!!$ 
!!$ 
!!$                           MLD2P4  version 2.0
!!$  MultiLevel Domain Decomposition Parallel Preconditioners Package
!!$             based on PSBLAS (Parallel Sparse BLAS version 3.0)
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!!$
!!$                      Salvatore Filippone  University of Rome Tor Vergata
!!$                      Alfredo Buttari      CNRS-IRIT, Toulouse
!!$                      Pasqua D'Ambra       ICAR-CNR, Naples
!!$                      Daniela di Serafino  Second University of Naples
!!$ 
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! File: mld_sslud_bld.f90
!
! Subroutine: mld_ssludist_bld
! Version:    real
!
!  This routine computes the LU factorization of of a distributed matrix,
!  by using SuperLU_DIST. 
!  
!  The matrix to be factorized is the coarsest-level matrix of a multilevel
!  preconditioner and is distributed among the processes. Its factorization
!  is used to build the 'base preconditioner' corresponding to the coarsest
!  level.
!
!  The data structure allocated by SuperLU_DIST to store the L and U factors
!  is pointed by p%iprcparm(mld_slud_ptr_).
!
!
! Arguments:
!    a       -  type(psb_sspmat_type), input/output.
!               The sparse matrix structure containing the local part of the
!               matrix to be factorized.
!    desc_a  -  type(psb_desc_type), input.
!               The communication descriptor associated to a.
!       p       -  type(mld_sbaseprec_type), input/output.
!               The 'base preconditioner' data structure containing the pointer, 
!               p%iprcparm(mld_slud_ptr_), to the data structure used by 
!               SuperLU_DIST to store the L and U factors.
!    info    -  integer, output.                                                             
!               Error code.
!  
subroutine mld_ssludist_bld(a,desc_a,p,info)

  use psb_sparse_mod
  use mld_s_inner_mod, mld_protect_name => mld_ssludist_bld

  implicit none

  ! Arguments
  type(psb_sspmat_type), intent(inout)   :: a
  type(psb_desc_type), intent(in)        :: desc_a
  type(mld_sbaseprec_type), intent(inout) :: p
  integer, intent(out)                   :: info

  ! Local variables
  integer            :: nzt,ictxt,me,np,err_act,&
       &                mglob,ifrst,ibcheck,nrow,ncol,npr,npc
  character(len=20)  :: name, ch_err

  if (psb_get_errstatus().ne.0) return 
  info=psb_success_
  name='mld_sslud_bld'
  call psb_erractionsave(err_act)

  ictxt = psb_cd_get_context(desc_a)

  call psb_info(ictxt, me, np)

  select type(aa=>a%a)
  type is (psb_s_csr_sparse_mat) 

    !
    ! WARN: we need to check for a BLOCK distribution (this is the
    ! distribution required by SuperLU_DIST)  
    !
    nrow = psb_cd_get_local_rows(desc_a)
    ncol = psb_cd_get_local_cols(desc_a)
    call psb_loc_to_glob(1,ifrst,desc_a,info) 
    call psb_loc_to_glob(nrow,ibcheck,desc_a,info) 
    ibcheck = ibcheck - ifrst + 1 
    ibcheck = ibcheck - nrow
    call psb_amx(ictxt,ibcheck)
    if (ibcheck > 0) then 
      write(0,*) 'Warning: does not look like a BLOCK distribution'
      info=psb_err_unsupported_format_
      ch_err = aa%get_fmt()
      call psb_errpush(info,name,a_err=ch_err)
      goto 9999
    endif

    mglob = psb_cd_get_global_rows(desc_a)
    nzt   = aa%get_nzeros()

    npr = np
    npc = 1
    call psb_loc_to_glob(aa%ja(1:nzt),desc_a,info,iact='I')

    !
    ! Compute the LU factorization
    !
    call mld_ssludist_fact(mglob,nrow,nzt,ifrst,&
         & aa%val,aa%irp,aa%ja,p%iprcparm(mld_slud_ptr_),&
         & npr, npc, info)
    if (info /= psb_success_) then
      ch_err='psb_sludist_fact'
      call psb_errpush(4110,name,a_err=ch_err,i_err=(/info,0,0,0,0/))
      goto 9999
    end if

    call psb_glob_to_loc(aa%ja(1:nzt),desc_a,info,iact='I')

  class default
    info=psb_err_unsupported_format_
    ch_err = aa%get_fmt()
    call psb_errpush(info,name,a_err=ch_err)
    goto 9999
  end select


  call psb_erractionrestore(err_act)
  return

9999 continue
  call psb_erractionrestore(err_act)
  if (err_act.eq.psb_act_abort_) then
    call psb_error()
    return
  end if
  return

end subroutine mld_ssludist_bld