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