pb_descinit2()

subroutine pb_descinit2	(	integer, dimension( * )	desc,
		integer	m,
		integer	n,
		integer	imb,
		integer	inb,
		integer	mb,
		integer	nb,
		integer	rsrc,
		integer	csrc,
		integer	ctxt,
		integer	lld,
		integer	info
	)

Definition at line 3335 of file pblastst.f.

*
*  -- PBLAS test routine (version 2.0) --
*     University of Tennessee, Knoxville, Oak Ridge National Laboratory,
*     and University of California, Berkeley.
*     April 1, 1998
*
*     .. Scalar Arguments ..
      INTEGER            CSRC, CTXT, IMB, INB, INFO, LLD, M, MB, N, NB,
     $                   RSRC
*     ..
*     .. Array Arguments ..
      INTEGER            DESC( * )
*     ..
*
*  Purpose
*  =======
*
*  PB_DESCINIT2 uses  its  10  input  arguments  M, N, IMB, INB, MB, NB,
*  RSRC,  CSRC,  CTXT  and LLD to initialize a descriptor vector of type
*  BLOCK_CYCLIC_2D_INB.
*
*  Notes
*  =====
*
*  A description  vector  is associated with each 2D block-cyclicly dis-
*  tributed matrix.  This  vector  stores  the  information  required to
*  establish the  mapping  between a  matrix entry and its corresponding
*  process and memory location.
*
*  In  the  following  comments,   the character _  should  be  read  as
*  "of  the  distributed  matrix".  Let  A  be a generic term for any 2D
*  block cyclicly distributed matrix.  Its description vector is DESCA:
*
*  NOTATION         STORED IN       EXPLANATION
*  ---------------- --------------- ------------------------------------
*  DTYPE_A (global) DESCA( DTYPE_ ) The descriptor type.
*  CTXT_A  (global) DESCA( CTXT_  ) The BLACS context handle, indicating
*                                   the NPROW x NPCOL BLACS process grid
*                                   A  is distributed over.  The context
*                                   itself  is  global,  but  the handle
*                                   (the integer value) may vary.
*  M_A     (global) DESCA( M_     ) The  number of rows in the distribu-
*                                   ted matrix A, M_A >= 0.
*  N_A     (global) DESCA( N_     ) The number of columns in the distri-
*                                   buted matrix A, N_A >= 0.
*  IMB_A   (global) DESCA( IMB_   ) The number of rows of the upper left
*                                   block of the matrix A, IMB_A > 0.
*  INB_A   (global) DESCA( INB_   ) The  number  of columns of the upper
*                                   left   block   of   the   matrix  A,
*                                   INB_A > 0.
*  MB_A    (global) DESCA( MB_    ) The blocking factor used to  distri-
*                                   bute the last  M_A-IMB_A rows of  A,
*                                   MB_A > 0.
*  NB_A    (global) DESCA( NB_    ) The blocking factor used to  distri-
*                                   bute the last  N_A-INB_A  columns of
*                                   A, NB_A > 0.
*  RSRC_A  (global) DESCA( RSRC_  ) The process row over which the first
*                                   row of the matrix  A is distributed,
*                                   NPROW > RSRC_A >= 0.
*  CSRC_A  (global) DESCA( CSRC_  ) The  process  column  over which the
*                                   first  column of  A  is distributed.
*                                   NPCOL > CSRC_A >= 0.
*  LLD_A   (local)  DESCA( LLD_   ) The  leading  dimension of the local
*                                   array  storing  the  local blocks of
*                                   the distributed matrix A,
*                                   IF( Lc( 1, N_A ) > 0 )
*                                      LLD_A >= MAX( 1, Lr( 1, M_A ) )
*                                   ELSE
*                                      LLD_A >= 1.
*
*  Let K be the number of  rows of a matrix A starting at the global in-
*  dex IA,i.e, A( IA:IA+K-1, : ). Lr( IA, K ) denotes the number of rows
*  that the process of row coordinate MYROW ( 0 <= MYROW < NPROW ) would
*  receive if these K rows were distributed over NPROW processes.  If  K
*  is the number of columns of a matrix  A  starting at the global index
*  JA, i.e, A( :, JA:JA+K-1, : ), Lc( JA, K ) denotes the number  of co-
*  lumns that the process MYCOL ( 0 <= MYCOL < NPCOL ) would  receive if
*  these K columns were distributed over NPCOL processes.
*
*  The values of Lr() and Lc() may be determined via a call to the func-
*  tion PB_NUMROC:
*  Lr( IA, K ) = PB_NUMROC( K, IA, IMB_A, MB_A, MYROW, RSRC_A, NPROW )
*  Lc( JA, K ) = PB_NUMROC( K, JA, INB_A, NB_A, MYCOL, CSRC_A, NPCOL )
*
*  Arguments
*  =========
*
*  DESC    (global and local output) INTEGER array
*          On entry, DESC is an array of  dimension  DLEN_.  DESC is the
*          array descriptor to be set.
*
*  M       (global input) INTEGER
*          On entry,  M  specifies  the  number  of  rows of the matrix.
*          M must be at least zero.
*
*  N       (global input) INTEGER
*          On entry,  N  specifies  the number of columns of the matrix.
*          N must be at least zero.
*
*  IMB     (global input) INTEGER
*          On entry,  IMB  specifies  the row size of the first block of
*          the global matrix distribution. IMB must be at least one.
*
*  INB     (global input) INTEGER
*          On entry,  INB  specifies  the column size of the first block
*          of the global matrix distribution. INB must be at least one.
*
*  MB      (global input) INTEGER
*          On entry,  MB  specifies  the  row size of the blocks used to
*          partition the matrix. MB must be at least one.
*
*  NB      (global input) INTEGER
*          On entry, NB  specifies the column size of the blocks used to
*          partition the matrix. NB must be at least one.
*
*  RSRC    (global input) INTEGER
*          On entry,  RSRC  specifies  the row coordinate of the process
*          that possesses the first row of the matrix.  When  RSRC = -1,
*          the data is not  distributed but replicated,  otherwise  RSRC
*          must be at least zero and strictly less than NPROW.
*
*  CSRC    (global input) INTEGER
*          On entry,  CSRC  specifies  the column coordinate of the pro-
*          cess  that  possesses  the  first column of the matrix.  When
*          CSRC = -1, the data is not distributed but replicated, other-
*          wise CSRC must be at least zero and strictly less than NPCOL.
*
*  CTXT    (local input) INTEGER
*          On entry, CTXT specifies the BLACS context handle, indicating
*          the global  communication  context.  The value of the context
*          itself is local.
*
*  LLD     (local input)  INTEGER
*          On entry, LLD  specifies  the  leading dimension of the local
*          array storing the local entries of the matrix. LLD must be at
*          least MAX( 1, Lr(1,M) ).
*
*  INFO    (local output) INTEGER
*          = 0: successful exit
*          < 0: if INFO = -i, the i-th argument had an illegal value.
*
*  Notes
*  =====
*
*  If the routine can recover from an erroneous input argument,  it will
*  return an acceptable descriptor vector.  For example,  if LLD = 0  on
*  input, DESC( LLD_ ) will  contain  the smallest leading dimension re-
*  quired to store the specified m by n matrix, INFO will however be set
*  to -11 on exit in that case.
*
*  -- Written on April 1, 1998 by
*     Antoine Petitet, University  of  Tennessee, Knoxville 37996, USA.
*
*  =====================================================================
*
*     .. Parameters ..
      INTEGER            BLOCK_CYCLIC_2D_INB, CSRC_, CTXT_, DLEN_,
     $                   DTYPE_, IMB_, INB_, LLD_, MB_, M_, NB_, N_,
     $                   RSRC_
      parameter( block_cyclic_2d_inb = 2, dlen_ = 11,
     $                   dtype_ = 1, ctxt_ = 2, m_ = 3, n_ = 4,
     $                   imb_ = 5, inb_ = 6, mb_ = 7, nb_ = 8,
     $                   rsrc_ = 9, csrc_ = 10, lld_ = 11 )
*     ..
*     .. Local Scalars ..
      INTEGER            LLDMIN, MP, MYCOL, MYROW, NPCOL, NPROW
*     ..
*     .. External Subroutines ..
      EXTERNAL           blacs_gridinfo, pxerbla
*     ..
*     .. External Functions ..
      INTEGER            PB_NUMROC
      EXTERNAL           pb_numroc
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          max, min
*     ..
*     .. Executable Statements ..
*
*     Get grid parameters
*
      CALL blacs_gridinfo( ctxt, nprow, npcol, myrow, mycol )
*
      info = 0
      IF( m.LT.0 ) THEN
         info = -2
      ELSE IF( n.LT.0 ) THEN
         info = -3
      ELSE IF( imb.LT.1 ) THEN
         info = -4
      ELSE IF( inb.LT.1 ) THEN
         info = -5
      ELSE IF( mb.LT.1 ) THEN
         info = -6
      ELSE IF( nb.LT.1 ) THEN
         info = -7
      ELSE IF( rsrc.LT.-1 .OR. rsrc.GE.nprow ) THEN
         info = -8
      ELSE IF( csrc.LT.-1 .OR. csrc.GE.npcol ) THEN
         info = -9
      ELSE IF( nprow.EQ.-1 ) THEN
         info = -10
      END IF
*
*     Compute minimum LLD if safe (to avoid division by 0)
*
      IF( info.EQ.0 ) THEN
         mp = pb_numroc( m, 1, imb, mb, myrow, rsrc, nprow )
         IF( pb_numroc( n, 1, inb, nb, mycol, csrc, npcol ).GT.0 ) THEN
            lldmin = max( 1, mp )
         ELSE
            lldmin = 1
         END IF
         IF( lld.LT.lldmin )
     $      info = -11
      END IF
*
      IF( info.NE.0 )
     $   CALL pxerbla( ctxt, 'PB_DESCINIT2', -info )
*
      desc( dtype_ ) = block_cyclic_2d_inb
      desc( ctxt_  ) = ctxt
      desc( m_     ) = max( 0, m )
      desc( n_     ) = max( 0, n )
      desc( imb_   ) = max( 1, imb )
      desc( inb_   ) = max( 1, inb )
      desc( mb_    ) = max( 1, mb )
      desc( nb_    ) = max( 1, nb )
      desc( rsrc_  ) = max( -1, min( rsrc, nprow-1 ) )
      desc( csrc_  ) = max( -1, min( csrc, npcol-1 ) )
      desc( lld_   ) = max( lld, lldmin )
*
      RETURN
*
*     End of PB_DESCINIT2
*

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