PDLARED1D(l) LAPACK routine (version 1.5) PDLARED1D(l)
NAME
PDLARED1D - redistribute a 1D array It assumes that the input array, BYCOL, is distributed across rows and that all process column contain
the same copy of BYCOL
SYNOPSIS
SUBROUTINE PDLARED1D( N, IA, JA, DESC, BYCOL, BYALL, WORK, LWORK )
INTEGER IA, JA, LWORK, N
INTEGER DESC( * )
DOUBLE PRECISION BYALL( * ), BYCOL( * ), WORK( LWORK )
PURPOSE
PDLARED1D redistributes a 1D array 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 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 BYCOL()
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 8
A 2D array descirptor, which describes BYCOL
BYCOL (local input) distributed block cyclic DOUBLE PRECISION array
global dimension (N), local dimension NP BYCOL is distributed across the process rows All process columns are assumed to contain
the same value
BYALL (global output) DOUBLE PRECISION 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) DOUBLE PRECISION dimension (LWORK)
Used to hold the buffers sent from one process to another
LWORK (local input) INTEGER size of WORK array
LWORK >= NUMROC(N, DESC( NB_ ), 0, 0, NPCOL)
LAPACK version 1.5 12 May 1997 PDLARED1D(l)