pslared2d (3)

SUBROUTINE PSLARED2D(

N, IA, JA, DESC, BYROW, BYALL, WORK, LWORK )

INTEGER

IA, JA, LWORK, N

INTEGER

DESC( * )

REAL

BYALL( * ), BYROW( * ), WORK( LWORK )

PSLARED2D 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 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

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)