PDLARED2D(l) ) PDLARED2D(l)NAME
PDLARED2D - 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
SYNOPSIS
SUBROUTINE PDLARED2D( N, IA, JA, DESC, BYROW, BYALL, WORK, LWORK )
INTEGER IA, JA, LWORK, N
INTEGER DESC( * )
DOUBLE PRECISION BYALL( * ), BYROW( * ), WORK( LWORK )
PURPOSE
PDLARED2D 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 vec‐
tor. This vector stores the information required to establish the map‐
ping 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 col‐
umn.
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 DOUBLE PRECISION array
global dimension (N), local dimension NP BYCOL is distributed
across the process columns All process rows are assumed to con‐
tain the same value
BYALL (global output) DOUBLE PRECISION global dimension( N )
local dimension (N) BYALL is exactly duplicated on all pro‐
cesses It contains the same values as BYCOL, but it is repli‐
cated 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) DOUBLE PRECISION 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)
ScaLAPACK version 1.7 13 August 2001 PDLARED2D(l)
