amg4psblas/mlprec/mld_scoarse_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_scoarse_bld.f90
!
! Subroutine: mld_scoarse_bld
! Version:    real
!
!  This routine builds the matrix associated to the current level of the
!  multilevel preconditioner from the matrix associated to the previous level,
!  by using a smoothed aggregation technique (therefore, it also builds the
!  prolongation and restriction operators mapping the current level to the
!  previous one and vice versa). Then the routine builds the base preconditioner
!  at the current level.
!  The current level is regarded as the coarse one, while the previous as
!  the fine one. This is in agreement with the fact that the routine is called,
!  by mld_mlprec_bld, only on levels >=2.
!
! 
! Arguments:
!    a       -  type(psb_sspmat_type).
!               The sparse matrix structure containing the local part of the
!               matrix to be preconditioned.
!    desc_a  -  type(psb_desc_type), input.
!               The communication descriptor of a.
!    p       -  type(mld_sonelev_type), input/output.
!               The 'one-level' data structure containing the local part
!               of the base preconditioner to be built as well as
!               information concerning the prolongator and its transpose.
!    info    -  integer, output.
!               Error code.         
!  
subroutine mld_scoarse_bld(a,desc_a,p,info)

  use psb_sparse_mod
  use mld_inner_mod, mld_protect_name => mld_scoarse_bld

  implicit none

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

  ! Local variables
  character(len=20)      :: name
  integer                :: ictxt, np, me, err_act
  integer, allocatable   :: ilaggr(:), nlaggr(:)

  name='mld_scoarse_bld'
  if (psb_get_errstatus().ne.0) return 
  call psb_erractionsave(err_act)
  info = psb_success_
  ictxt = psb_cd_get_context(desc_a)
  call psb_info(ictxt,me,np)

  if (.not.allocated(p%iprcparm)) then 
    info = 2222
    call psb_errpush(info,name)
    goto 9999
  endif
  call mld_check_def(p%iprcparm(mld_ml_type_),'Multilevel type',&
       &   mld_mult_ml_,is_legal_ml_type)
  call mld_check_def(p%iprcparm(mld_aggr_alg_),'Aggregation',&
       &   mld_dec_aggr_,is_legal_ml_aggr_alg)
  call mld_check_def(p%iprcparm(mld_aggr_kind_),'Smoother',&
       &   mld_smooth_prol_,is_legal_ml_aggr_kind)
  call mld_check_def(p%iprcparm(mld_coarse_mat_),'Coarse matrix',&
       &   mld_distr_mat_,is_legal_ml_coarse_mat)
  call mld_check_def(p%iprcparm(mld_aggr_filter_),'Use filtered matrix',&
       &   mld_no_filter_mat_,is_legal_aggr_filter)
  call mld_check_def(p%iprcparm(mld_smoother_pos_),'smooth_pos',&
       &   mld_pre_smooth_,is_legal_ml_smooth_pos)
  call mld_check_def(p%iprcparm(mld_aggr_omega_alg_),'Omega Alg.',&
       &   mld_eig_est_,is_legal_ml_aggr_omega_alg)
  call mld_check_def(p%iprcparm(mld_aggr_eig_),'Eigenvalue estimate',&
       &   mld_max_norm_,is_legal_ml_aggr_eig)
  call mld_check_def(p%rprcparm(mld_aggr_omega_val_),'Omega',szero,is_legal_s_omega)
  call mld_check_def(p%rprcparm(mld_aggr_thresh_),'Aggr_Thresh',szero,is_legal_s_aggr_thrs)
  

  !
  !  Build a mapping between the row indices of the fine-level matrix 
  !  and the row indices of the coarse-level matrix, according to a decoupled 
  !  aggregation algorithm. This also defines a tentative prolongator from
  !  the coarse to the fine level.
  ! 
  call mld_aggrmap_bld(p%iprcparm(mld_aggr_alg_),p%rprcparm(mld_aggr_thresh_),&
       & a,desc_a,ilaggr,nlaggr,info)

  if (info /= psb_success_) then
    call psb_errpush(psb_err_from_subroutine_,name,a_err='mld_aggrmap_bld')
    goto 9999
  end if

  !
  ! Build the coarse-level matrix from the fine-level one, starting from 
  ! the mapping defined by mld_aggrmap_bld and applying the aggregation
  ! algorithm specified by p%iprcparm(mld_aggr_kind_)
  !
  call mld_aggrmat_asb(a,desc_a,ilaggr,nlaggr,p,info)

  if(info /= psb_success_) then
    call psb_errpush(psb_err_from_subroutine_,name,a_err='mld_aggrmat_asb')
    goto 9999
  end if
  !
  ! Fix the base_a and base_desc pointers for handling of residuals.
  ! This is correct because this routine is only called at levels >=2.
  !
  p%base_a    => p%ac
  p%base_desc => p%desc_ac
  
  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_scoarse_bld