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SUBROUTINE PSROW2COL( ICTXT, M, N, NB, VS, LDVS, VD, LDVD,
$ RSRC, CSRC, RDEST, CDEST, WORK)
*
* -- 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 CDEST, CSRC, ICTXT, LDVD, LDVS, M, N, NB,
$ RDEST, RSRC
* ..
* .. Array Arguments ..
REAL VD( LDVD, * ), VS( LDVS, * ), WORK( * )
* ..
*
* Purpose
* =======
*
* Take a block of vectors with M total rows which are distributed over
* a row of processes, and distribute those rows over a column of
* processes. This routine minimizes communication by sending all
* information it has that a given process in the CDEST needs at once.
* To do this it uses the least common multiple (LCM) concept. This is
* simply the realization that if I have part of a vector split over a
* process row consisting of Q processes, and I want to send all of that
* vector that I own to a new vector distributed over P processes within
* a process column, that after I find the process in RDEST that owns
* the row of the vector I'm currently looking at, he will want every
* ( (LCM(P,Q)/Q ) block of my vector (the block being of size NB x N).
*
* Arguments
* =========
*
* Rem: MP, resp. NQ, denotes the number of local rows, resp. local
* ==== columns, necessary to store a global vector of dimension M
* across P processes, resp. N over Q processes.
*
* ICTXT (global input) INTEGER
* The BLACS context handle, indicating the global context of
* the operation. The context itself is global.
*
* M (global input) INTEGER
* The number of global rows each vector has.
*
* N (global input) INTEGER
* The number of vectors in the vector block
*
* NB (global input) INTEGER
* The blocking factor used to divide the rows of the vector
* amongst the processes of a row.
*
* VS (local input) REAL
* Array of dimension (LDVS,N), the block of vectors stored on
* process row RSRC to be put into memory VD, and stored on
* process column CDEST.
*
* LDVS (local input) INTEGER
* The leading dimension of VS.
*
* VD (local output) REAL
* Array of dimension (LDVD,N), on output, the contents of VD
* stored on process column CDEST will be here.
*
* LDVD (local input) INTEGER
* The leading dimension of VD.
*
* RSRC (global input) INTEGER
* The process row VS is distributed over.
*
* CSRC (global input) INTEGER
* The process column the distributed block of vectors VS
* begins on.
*
* RDEST (global input) INTEGER
* The process row that VD begins on.
*
* CDEST (global input) INTEGER
* The process column to distribute VD over.
*
* WORK (local workspace) REAL
* Array, dimension (LDW). The required size of work varies:
* if( nprow.eq.npcol ) then
* LDW = 0; WORK not accessed.
* else
* lcm = least common multiple of process rows and columns.
* Mq = number of rows of VS on my process.
* npcol = number of process columns
* CEIL = the ceiling of given operation
* LDW = NB*N*CEIL( CEIL( Mq/NB )/(LCM/npcol) )
* end if
*
* =====================================================================
*
* .. Local Scalars ..
INTEGER CBLKSKIP, ICPY, II, ISTART, ICSRC, IRDEST, JB,
$ JJ, K, LCM, MP, MQ, MYCOL, MYDIST, MYROW,
$ NBLOCKS, NPCOL, NPROW, RBLKSKIP
* ..
* .. External Subroutines ..
EXTERNAL BLACS_GRIDINFO, SGESD2D, SGERV2D, SLACPY
* ..
* .. External Functions ..
INTEGER ILCM, NUMROC
EXTERNAL ILCM, NUMROC
* ..
* .. Executable Statements ..
*
*
* .. Initialize Variables ..
*
ICPY = 0
*
CALL BLACS_GRIDINFO( ICTXT, NPROW, NPCOL, MYROW, MYCOL )
*
* If we are not in special case for NPROW = NPCOL where there is no
* copying required
*
IF( NPROW .NE. NPCOL ) THEN
LCM = ILCM( NPROW, NPCOL )
RBLKSKIP = LCM / NPCOL
CBLKSKIP = LCM / NPROW
*
* If I have part of VS, the source vector(s)
*
IF( MYROW.EQ.RSRC ) THEN
*
ISTART = 1
*
* Figure my distance from CSRC: the process in CDEST the same
* distance from RDEST will want my first block
*
MYDIST = MOD( NPCOL+MYCOL-CSRC, NPCOL )
MQ = NUMROC( M, NB, MYCOL, CSRC, NPCOL )
IRDEST = MOD( RDEST+MYDIST, NPROW )
*
* Loop over all possible destination processes
*
DO 20 K = 1, RBLKSKIP
JJ = 1
*
* If I am not destination process
*
IF( (MYROW.NE.IRDEST).OR.(MYCOL.NE.CDEST) ) THEN
*
* Pack all data I own that destination needs
*
DO 10 II = ISTART, MQ, NB*RBLKSKIP
JB = MIN( NB, MQ-II+1 )
CALL SLACPY( 'G', JB, N, VS(II,1), LDVS,
$ WORK(JJ), JB )
JJ = JJ + NB*N
10 CONTINUE
*
* Figure how many rows are to be sent and send them if
* necessary, NOTE: will send extra if NB > JB
*
JJ = JJ - 1
IF( JJ.GT.0 )
$ CALL SGESD2D( ICTXT, JJ, 1, WORK, JJ, IRDEST,
$ CDEST )
*
* I am both source and destination, save where to start
* copying from for later use
*
ELSE
ICPY = ISTART
END IF
*
ISTART = ISTART + NB
IRDEST = MOD( IRDEST+NPCOL, NPROW )
20 CONTINUE
END IF
*
* If I should receive info into VD
*
IF( MYCOL.EQ.CDEST ) THEN
*
ISTART = 1
*
* Figure my distance from CDEST: the process in CSRC the same
* distance from RSRC will have my first block
*
MYDIST = MOD( NPROW+MYROW-RDEST, NPROW )
MP = NUMROC( M, NB, MYROW, RDEST, NPROW )
ICSRC = MOD( CSRC+MYDIST, NPCOL )
*
* Loop over all sending processes
*
DO 50 K = 1, CBLKSKIP
*
* If I don't already possess the required data
*
IF( (MYROW.NE.RSRC).OR.(MYCOL.NE.ICSRC) ) THEN
*
* Figure how many rows to receive, and receive them
* NOTE: may receive to much -- NB instead of JB
*
NBLOCKS = (MP - ISTART + NB) / NB
JJ = ((NBLOCKS+CBLKSKIP-1) / CBLKSKIP)*NB
IF( JJ.GT.0 )
$ CALL SGERV2D( ICTXT, JJ, N, WORK, JJ, RSRC, ICSRC )
*
* Copy data to destination vector
*
JJ = 1
DO 30 II = ISTART, MP, NB*CBLKSKIP
JB = MIN( NB, MP-II+1 )
CALL SLACPY( 'G', JB, N, WORK(JJ), JB, VD(II,1),
$ LDVD )
JJ = JJ + NB*N
30 CONTINUE
*
* If I am both source and destination
*
ELSE
JJ = ICPY
DO 40 II = ISTART, MP, NB*CBLKSKIP
JB = MIN( NB, MP-II+1 )
CALL SLACPY( 'G', JB, N, VS(JJ,1), LDVS, VD(II,1),
$ LDVD )
JJ = JJ + NB*RBLKSKIP
40 CONTINUE
END IF
ISTART = ISTART + NB
ICSRC = MOD( ICSRC+NPROW, NPCOL )
50 CONTINUE
END IF
*
* if NPROW = NPCOL, there is a one-to-one correspondance between
* process rows and columns, so no work space or copying required
*
ELSE
*
IF( MYROW.EQ.RSRC ) THEN
*
* Figure my distance from CSRC: the process in CDEST the same
* distance from RDEST will want my piece of the vector
*
MYDIST = MOD( NPCOL+MYCOL-CSRC, NPCOL )
MQ = NUMROC( M, NB, MYCOL, CSRC, NPCOL )
IRDEST = MOD( RDEST+MYDIST, NPROW )
IF( (MYROW.NE.IRDEST).OR.(MYCOL.NE.CDEST) ) THEN
CALL SGESD2D( ICTXT, MQ, N, VS, LDVS, IRDEST, CDEST )
ELSE
CALL SLACPY( 'G', MQ, N, VS, LDVS, VD, LDVD )
END IF
END IF
IF( MYCOL.EQ.CDEST ) THEN
*
* Figure my distance from RDEST: the process in RSRC the same
* distance from CSRC will have my piece of the vector
*
MYDIST = MOD( NPROW+MYROW-RDEST, NPROW )
MP = NUMROC( M, NB, MYROW, RDEST, NPROW )
ICSRC = MOD( CSRC+MYDIST, NPCOL )
IF( (MYCOL.NE.ICSRC).OR.(MYROW.NE. RSRC) )
$ CALL SGERV2D( ICTXT, MP, N, VD, LDVD, RSRC, ICSRC )
END IF
END IF
*
RETURN
*
* End of PSROW2COL
*
END
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