SUBROUTINE PSELGET( SCOPE, TOP, ALPHA, A, IA, JA, DESCA ) * * -- ScaLAPACK tools routine (version 1.7) -- * University of Tennessee, Knoxville, Oak Ridge National Laboratory, * and University of California, Berkeley. * May 1, 1997 * * .. Scalar Arguments .. CHARACTER*1 SCOPE, TOP INTEGER IA, JA REAL ALPHA * .. * .. Array arguments .. INTEGER DESCA( * ) REAL A( * ) * .. * * Purpose * ======= * * PSELGET sets alpha to the distributed matrix entry A( IA, JA ). * The value of alpha is set according to the scope. * * 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 * ========= * * SCOPE (global input) CHARACTER*1 * The BLACS scope in which alpha is updated. * If SCOPE = 'R', alpha is updated only in the process row * containing A( IA, JA ), * If SCOPE = 'C', alpha is updated only in the process column * containing A( IA, JA ), * If SCOPE = 'A', alpha is updated in all the processes of the * grid, * otherwise alpha is updated only in the process containing * A( IA, JA ). * * TOP (global input) CHARACTER*1 * The topology to be used if broadcast is needed. * * ALPHA (global output) REAL, the scalar alpha. * * A (local input) REAL pointer into the local memory * to an array of dimension (LLD_A,*) containing the local * pieces of the distributed matrix A. * * IA (global input) INTEGER * The row index in the global array A indicating the first * row of sub( A ). * * JA (global input) INTEGER * The column index in the global array A indicating the * first column of sub( A ). * * DESCA (global and local input) INTEGER array of dimension DLEN_. * The array descriptor for the distributed matrix A. * * ===================================================================== * * .. 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 ) REAL ZERO PARAMETER ( ZERO = 0.0E+0 ) * .. * .. Local Scalars .. INTEGER IACOL, IAROW, ICTXT, IIA, IOFFA, JJA, MYCOL, $ MYROW, NPCOL, NPROW * .. * .. External Subroutines .. EXTERNAL BLACS_GRIDINFO, INFOG2L, SGEBR2D, SGEBS2D * .. * .. External Functions .. LOGICAL LSAME EXTERNAL LSAME * .. * .. Executable Statements .. * * Get grid parameters. * ICTXT = DESCA( CTXT_ ) CALL BLACS_GRIDINFO( ICTXT, NPROW, NPCOL, MYROW, MYCOL ) * CALL INFOG2L( IA, JA, DESCA, NPROW, NPCOL, MYROW, MYCOL, IIA, JJA, $ IAROW, IACOL ) * ALPHA = ZERO * IF( LSAME( SCOPE, 'R' ) ) THEN IF( MYROW.EQ.IAROW ) THEN IF( MYCOL.EQ.IACOL ) THEN IOFFA = IIA+(JJA-1)*DESCA( LLD_ ) CALL SGEBS2D( ICTXT, SCOPE, TOP, 1, 1, A( IOFFA ), 1 ) ALPHA = A( IOFFA ) ELSE CALL SGEBR2D( ICTXT, SCOPE, TOP, 1, 1, ALPHA, 1, $ IAROW, IACOL ) END IF END IF ELSE IF( LSAME( SCOPE, 'C' ) ) THEN IF( MYCOL.EQ.IACOL ) THEN IF( MYROW.EQ.IAROW ) THEN IOFFA = IIA+(JJA-1)*DESCA( LLD_ ) CALL SGEBS2D( ICTXT, SCOPE, TOP, 1, 1, A( IOFFA ), 1 ) ALPHA = A( IOFFA ) ELSE CALL SGEBR2D( ICTXT, SCOPE, TOP, 1, 1, ALPHA, 1, $ IAROW, IACOL ) END IF END IF ELSE IF( LSAME( SCOPE, 'A' ) ) THEN IF( ( MYROW.EQ.IAROW ).AND.( MYCOL.EQ.IACOL ) ) THEN IOFFA = IIA+(JJA-1)*DESCA( LLD_ ) CALL SGEBS2D( ICTXT, SCOPE, TOP, 1, 1, A( IOFFA ), 1 ) ALPHA = A( IOFFA ) ELSE CALL SGEBR2D( ICTXT, SCOPE, TOP, 1, 1, ALPHA, 1, $ IAROW, IACOL ) END IF ELSE IF( MYROW.EQ.IAROW .AND. MYCOL.EQ.IACOL ) $ ALPHA = A( IIA+(JJA-1)*DESCA( LLD_ ) ) END IF * RETURN * * End of PSELGET * END