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PDLASCL

PDLASCL

Section: LAPACK auxiliary routine (version 1.5) (l) Updated: 12 May 1997
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NAME

PDLASCL - multiplie the M-by-N real distributed matrix sub( A ) denoting A(IA:IA+M-1,JA:JA+N-1) by the real scalar CTO/CFROM  

SYNOPSIS

SUBROUTINE PDLASCL(
TYPE, CFROM, CTO, M, N, A, IA, JA, DESCA, INFO )

    
CHARACTER TYPE

    
INTEGER IA, INFO, JA, M, N

    
DOUBLE PRECISION CFROM, CTO

    
INTEGER DESCA( * )

    
DOUBLE PRECISION A( * )
 

PURPOSE

PDLASCL multiplies the M-by-N real distributed matrix sub( A ) denoting A(IA:IA+M-1,JA:JA+N-1) by the real scalar CTO/CFROM. This is done without over/underflow as long as the final result CTO * A(I,J) / CFROM does not over/underflow. TYPE specifies that sub( A ) may be full, upper triangular, lower triangular or upper Hessenberg.

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

TYPE (global input) CHARACTER
TYPE indices the storage type of the input distributed matrix. = 'G': sub( A ) is a full matrix,
= 'L': sub( A ) is a lower triangular matrix,
= 'U': sub( A ) is an upper triangular matrix,
= 'H': sub( A ) is an upper Hessenberg matrix.
CFROM (global input) DOUBLE PRECISION
CTO (global input) DOUBLE PRECISION The distributed matrix sub( A ) is multiplied by CTO/CFROM. A(I,J) is computed without over/underflow if the final result CTO * A(I,J) / CFROM can be represented without over/underflow. CFROM must be nonzero.
M (global input) INTEGER
The number of rows to be operated on i.e the number of rows of the distributed submatrix sub( A ). M >= 0.
N (global input) INTEGER
The number of columns to be operated on i.e the number of columns of the distributed submatrix sub( A ). N >= 0.
A (local input/local output) DOUBLE PRECISION pointer into the
local memory to an array of dimension (LLD_A,LOCc(JA+N-1)). This array contains the local pieces of the distributed matrix sub( A ). On exit, this array contains the local pieces of the distributed matrix multiplied by CTO/CFROM.
IA (global input) INTEGER
The row index in the global array A indicating the first row of sub( A ).
JA (global input) INTEGER
The column index in the global array A indicating the first column of sub( A ).
DESCA (global and local input) INTEGER array of dimension DLEN_.
The array descriptor for the distributed matrix A.
INFO (local output) INTEGER
= 0: successful exit
< 0: If the i-th argument is an array and the j-entry had an illegal value, then INFO = -(i*100+j), if the i-th argument is a scalar and had an illegal value, then INFO = -i.


 

Index

NAME
SYNOPSIS
PURPOSE
ARGUMENTS

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