NAME
PCLASCL - multiplie the M-by-N complex distributed matrix sub( A )
denoting A(IA:IA+M-1,JA:JA+N-1) by the real scalar CTO/CFROM
SYNOPSIS
SUBROUTINE PCLASCL( TYPE, CFROM, CTO, M, N, A, IA, JA, DESCA, INFO )
CHARACTER TYPE
INTEGER IA, INFO, JA, M, N
REAL CFROM, CTO
INTEGER DESCA( * )
COMPLEX A( * )
PURPOSE
PCLASCL multiplies the M-by-N complex 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) REAL
CTO (global input) REAL 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) COMPLEX 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.