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SUBROUTINE DESCINIT( DESC, M, N, MB, NB, IRSRC, ICSRC, ICTXT,
$ LLD, INFO )
*
* -- ScaLAPACK tools routine (version 1.7) --
* University of Tennessee, Knoxville, Oak Ridge National Laboratory,
* and University of California, Berkeley.
* May 1, 1997
*
* .. Scalar Arguments ..
INTEGER ICSRC, ICTXT, INFO, IRSRC, LLD, M, MB, N, NB
* ..
* .. Array Arguments ..
INTEGER DESC( * )
* ..
*
* Purpose
* =======
*
* DESCINIT initializes the descriptor vector with the 8 input arguments
* M, N, MB, NB, IRSRC, ICSRC, ICTXT, LLD.
*
* Notes
* =====
*
* Each global data object is described by an associated description
* vector. This vector stores the information required to establish
* the mapping between an object element and its corresponding process
* and memory location.
*
* Let A be a generic term for any 2D block cyclicly distributed array.
* Such a global array has an associated description vector DESCA.
* In the following comments, the character _ should be read as
* "of the global array".
*
* NOTATION STORED IN EXPLANATION
* --------------- -------------- --------------------------------------
* DTYPE_A(global) DESCA( DTYPE_ )The descriptor type. In this case,
* DTYPE_A = 1.
* CTXT_A (global) DESCA( CTXT_ ) The BLACS context handle, indicating
* the BLACS process grid A is distribu-
* ted over. The context itself is glo-
* bal, but the handle (the integer
* value) may vary.
* M_A (global) DESCA( M_ ) The number of rows in the global
* array A.
* N_A (global) DESCA( N_ ) The number of columns in the global
* array A.
* MB_A (global) DESCA( MB_ ) The blocking factor used to distribute
* the rows of the array.
* NB_A (global) DESCA( NB_ ) The blocking factor used to distribute
* the columns of the array.
* RSRC_A (global) DESCA( RSRC_ ) The process row over which the first
* row of the array A is distributed.
* CSRC_A (global) DESCA( CSRC_ ) The process column over which the
* first column of the array A is
* distributed.
* LLD_A (local) DESCA( LLD_ ) The leading dimension of the local
* array. LLD_A >= MAX(1,LOCr(M_A)).
*
* Let K be the number of rows or columns of a distributed matrix,
* and assume that its process grid has dimension p x q.
* LOCr( K ) denotes the number of elements of K that a process
* would receive if K were distributed over the p processes of its
* process column.
* Similarly, LOCc( K ) denotes the number of elements of K that a
* process would receive if K were distributed over the q processes of
* its process row.
* The values of LOCr() and LOCc() may be determined via a call to the
* ScaLAPACK tool function, NUMROC:
* LOCr( M ) = NUMROC( M, MB_A, MYROW, RSRC_A, NPROW ),
* LOCc( N ) = NUMROC( N, NB_A, MYCOL, CSRC_A, NPCOL ).
* An upper bound for these quantities may be computed by:
* LOCr( M ) <= ceil( ceil(M/MB_A)/NPROW )*MB_A
* LOCc( N ) <= ceil( ceil(N/NB_A)/NPCOL )*NB_A
*
* Arguments
* =========
*
* DESC (output) INTEGER array of dimension DLEN_.
* The array descriptor of a distributed matrix to be set.
*
* M (global input) INTEGER
* The number of rows in the distributed matrix. M >= 0.
*
* N (global input) INTEGER
* The number of columns in the distributed matrix. N >= 0.
*
* MB (global input) INTEGER
* The blocking factor used to distribute the rows of the
* matrix. MB >= 1.
*
* NB (global input) INTEGER
* The blocking factor used to distribute the columns of the
* matrix. NB >= 1.
*
* IRSRC (global input) INTEGER
* The process row over which the first row of the matrix is
* distributed. 0 <= IRSRC < NPROW.
*
* ICSRC (global input) INTEGER
* The process column over which the first column of the
* matrix is distributed. 0 <= ICSRC < NPCOL.
*
* ICTXT (global input) INTEGER
* The BLACS context handle, indicating the global context of
* the operation on the matrix. The context itself is global.
*
* LLD (local input) INTEGER
* The leading dimension of the local array storing the local
* blocks of the distributed matrix. LLD >= MAX(1,LOCr(M)).
*
* INFO (output) INTEGER
* = 0: successful exit
* < 0: if INFO = -i, the i-th argument had an illegal value
*
* Note
* ====
*
* 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
* required to store the specified M-by-N distributed matrix, INFO
* will be set -9 in that case.
*
* =====================================================================
*
* .. Parameters ..
INTEGER BLOCK_CYCLIC_2D, CSRC_, CTXT_, DLEN_, DTYPE_,
$ LLD_, MB_, M_, NB_, N_, RSRC_
PARAMETER ( BLOCK_CYCLIC_2D = 1, DLEN_ = 9, DTYPE_ = 1,
$ CTXT_ = 2, M_ = 3, N_ = 4, MB_ = 5, NB_ = 6,
$ RSRC_ = 7, CSRC_ = 8, LLD_ = 9 )
* ..
* .. Local Scalars ..
INTEGER MYCOL, MYROW, NPCOL, NPROW
* ..
* .. External Subroutines ..
EXTERNAL BLACS_GRIDINFO, PXERBLA
* ..
* .. External Functions ..
INTEGER NUMROC
EXTERNAL NUMROC
* ..
* .. Intrinsic Functions ..
INTRINSIC MAX, MIN
* ..
* .. Executable Statements ..
*
* Get grid parameters
*
CALL BLACS_GRIDINFO( ICTXT, NPROW, NPCOL, MYROW, MYCOL )
*
INFO = 0
IF( M.LT.0 ) THEN
INFO = -2
ELSE IF( N.LT.0 ) THEN
INFO = -3
ELSE IF( MB.LT.1 ) THEN
INFO = -4
ELSE IF( NB.LT.1 ) THEN
INFO = -5
ELSE IF( IRSRC.LT.0 .OR. IRSRC.GE.NPROW ) THEN
INFO = -6
ELSE IF( ICSRC.LT.0 .OR. ICSRC.GE.NPCOL ) THEN
INFO = -7
ELSE IF( NPROW.EQ.-1 ) THEN
INFO = -8
ELSE IF( LLD.LT.MAX( 1, NUMROC( M, MB, MYROW, IRSRC,
$ NPROW ) ) ) THEN
INFO = -9
END IF
*
IF( INFO.NE.0 )
$ CALL PXERBLA( ICTXT, 'DESCINIT', -INFO )
*
DESC( DTYPE_ ) = BLOCK_CYCLIC_2D
DESC( M_ ) = MAX( 0, M )
DESC( N_ ) = MAX( 0, N )
DESC( MB_ ) = MAX( 1, MB )
DESC( NB_ ) = MAX( 1, NB )
DESC( RSRC_ ) = MAX( 0, MIN( IRSRC, NPROW-1 ) )
DESC( CSRC_ ) = MAX( 0, MIN( ICSRC, NPCOL-1 ) )
DESC( CTXT_ ) = ICTXT
DESC( LLD_ ) = MAX( LLD, MAX( 1, NUMROC( DESC( M_ ), DESC( MB_ ),
$ MYROW, DESC( RSRC_ ), NPROW ) ) )
*
RETURN
*
* End DESCINIT
*
END
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