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Man Pages


Manual Reference Pages  -  PSLARED2D (l)

NAME

PSLARED2D - redistribute a 1D array It assumes that the input array, BYROW, is distributed across columns and that all process rows contain the same copy of BYROW

CONTENTS

Synopsis
Purpose
Arguments

SYNOPSIS

SUBROUTINE PSLARED2D( N, IA, JA, DESC, BYROW, BYALL, WORK, LWORK )
    INTEGER IA, JA, LWORK, N
    INTEGER DESC( * )
    REAL BYALL( * ), BYROW( * ), WORK( LWORK )

PURPOSE

PSLARED2D redistributes a 1D array It assumes that the input array, BYROW, is distributed across columns and that all process rows contain the same copy of BYROW. The output array, BYALL, will be identical on all processes and will contain the entire array.

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

NP = Number of local rows in BYROW()
N (global input) INTEGER
  The number of elements to be redistributed. N >= 0.
IA (global input) INTEGER
  IA must be equal to 1
JA (global input) INTEGER
  JA must be equal to 1
DESC (global/local input) INTEGER Array of dimension DLEN_
  A 2D array descriptor, which describes BYROW
BYROW (local input) distributed block cyclic REAL array
  global dimension (N), local dimension NP BYCOL is distributed across the process columns All process rows are assumed to contain the same value
BYALL (global output) REAL global dimension( N )
  local dimension (N) BYALL is exactly duplicated on all processes It contains the same values as BYCOL, but it is replicated across all processes rather than being distributed

BYALL(i) = BYCOL( NUMROC(i,NB,MYROW,0,NPROW ) on the procs whose MYROW == mod((i-1)/NB,NPROW)

WORK (local workspace) REAL dimension (LWORK)
  Used to hold the buffers sent from one process to another
LWORK (local input) INTEGER size of WORK array LWORK >=
  LWORK >= NUMROC(N, DESC( NB_ ), 0, 0, NPCOL)

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ScaLAPACK version 1.7 PSLARED2D (l) 13 August 2001

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