SUBROUTINE INFOG2L( GRINDX, GCINDX, DESC, NPROW, NPCOL, MYROW, $ MYCOL, LRINDX, LCINDX, RSRC, CSRC ) * * -- 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 CSRC, GCINDX, GRINDX, LRINDX, LCINDX, MYCOL, $ MYROW, NPCOL, NPROW, RSRC * .. * .. Array Arguments .. INTEGER DESC( * ) * .. * * Purpose * ======= * * INFOG2L computes the starting local indexes LRINDX, LCINDX corres- * ponding to the distributed submatrix starting globally at the entry * pointed by GRINDX, GCINDX. This routine returns the coordinates in * the grid of the process owning the matrix entry of global indexes * GRINDX, GCINDX, namely RSRC and CSRC. * * 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 * ========= * * GRINDX (global input) INTEGER * The global row starting index of the submatrix. * * GCINDX (global input) INTEGER * The global column starting index of the submatrix. * * DESC (input) INTEGER array of dimension DLEN_. * The array descriptor for the underlying distributed matrix. * * NPROW (global input) INTEGER * The total number of process rows over which the distributed * matrix is distributed. * * NPCOL (global input) INTEGER * The total number of process columns over which the * distributed matrix is distributed. * * MYROW (local input) INTEGER * The row coordinate of the process calling this routine. * * MYCOL (local input) INTEGER * The column coordinate of the process calling this routine. * * LRINDX (local output) INTEGER * The local rows starting index of the submatrix. * * LCINDX (local output) INTEGER * The local columns starting index of the submatrix. * * RSRC (global output) INTEGER * The row coordinate of the process that possesses the first * row and column of the submatrix. * * CSRC (global output) INTEGER * The column coordinate of the process that possesses the * first row and column of the submatrix. * * ===================================================================== * * .. 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 CBLK, GCCPY, GRCPY, RBLK * .. * .. Intrinsic Functions .. INTRINSIC MOD * .. * .. Executable Statements .. * GRCPY = GRINDX-1 GCCPY = GCINDX-1 * RBLK = GRCPY / DESC(MB_) CBLK = GCCPY / DESC(NB_) RSRC = MOD( RBLK + DESC(RSRC_), NPROW ) CSRC = MOD( CBLK + DESC(CSRC_), NPCOL ) * LRINDX = ( RBLK / NPROW + 1 ) * DESC(MB_) + 1 LCINDX = ( CBLK / NPCOL + 1 ) * DESC(NB_) + 1 * IF( MOD( MYROW+NPROW-DESC(RSRC_), NPROW ) .GE. $ MOD( RBLK, NPROW ) ) THEN IF( MYROW.EQ.RSRC ) $ LRINDX = LRINDX + MOD( GRCPY, DESC(MB_) ) LRINDX = LRINDX - DESC(MB_) END IF * IF( MOD( MYCOL+NPCOL-DESC(CSRC_), NPCOL ) .GE. $ MOD( CBLK, NPCOL ) ) THEN IF( MYCOL.EQ.CSRC ) $ LCINDX = LCINDX + MOD( GCCPY, DESC(NB_) ) LCINDX = LCINDX - DESC(NB_) END IF * RETURN * * End of INFOG2L * END