$Id: pdgemr.c,v 1.1.1.1 2000/02/15 18:04:09 susan Exp $
– ScaLAPACK routine (version 1.7) – Oak Ridge National Laboratory, Univ. of Tennessee, and Univ. of California, Berkeley. October 31, 1994.
SUBROUTINE PDGEMR2D( M, N, $ A, IA, JA, ADESC, $ B, IB, JB, BDESC,
$ CTXT)
Purpose
PDGEMR2D copies a submatrix of A on a submatrix of B. A and B can have different distributions: they can be on different processor grids, they can have different blocksizes, the beginning of the area to be copied can be at a different places on A and B.
The parameters can be confusing when the grids of A and B are partially or completly disjoint, in the case a processor calls this routines but is either not in the A context or B context, the ADESC[CTXT] or BDESC[CTXT] must be equal to -1, to ensure the routine recognise this situation. To summarize the rule:
- If a processor is in A context, all parameters related to A must be valid.
- If a processor is in B context, all parameters related to B must be valid.
- ADESC[CTXT] and BDESC[CTXT] must be either valid contexts or equal to -1.
- M and N must be valid for everyone.
- other parameters are not examined.
Notes
A description vector is associated with each 2D block-cyclicly dis- tributed matrix. This vector stores the information required to establish the mapping between a matrix entry and its corresponding process and memory location.
In the following comments, the character _ should be read as "of the distributed matrix". Let A be a generic term for any 2D block cyclicly distributed matrix. Its description vector is DESC_A:
NOTATION STORED IN EXPLANATION
DT_A (global) DESCA( DT_ ) The descriptor type. 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 distributed matrix A. N_A (global) DESCA( N_ ) The number of columns in the distri- buted matrix A. MB_A (global) DESCA( MB_ ) The blocking factor used to distribute the rows of A. NB_A (global) DESCA( NB_ ) The blocking factor used to distribute the columns of A. RSRC_A (global) DESCA( RSRC_ ) The process row over which the first row of the matrix A is distributed. CSRC_A (global) DESCA( CSRC_ ) The process column over which the first column of A is distributed. LLD_A (local) DESCA( LLD_ ) The leading dimension of the local array storing the local blocks of the distributed matrix A. LLD_A >= MAX(1,LOCp(M_A)).
Important notice
The parameters of the routine have changed in April 1996 There is a new last argument. It must be a context englobing all processors involved in the initial and final distribution.
Be aware that all processors included in this context must call the redistribution routine.
Parameters
M (input) INTEGER. On entry, M specifies the number of rows of the submatrix to be copied. M must be at least zero. Unchanged on exit.
N (input) INTEGER. On entry, N specifies the number of cols of the submatrix to be redistributed.rows of B. M must be at least zero. Unchanged on exit.
A (input) DOUBLE PRECISION On entry, the source matrix. Unchanged on exit.
IA,JA (input) INTEGER On entry,the coordinates of the beginning of the submatrix of A to copy. 1 <= IA <= M_A - M + 1,1 <= JA <= N_A - N + 1, Unchanged on exit.
ADESC (input) A description vector (see Notes above) If the current processor is not part of the context of A the ADESC[CTXT] must be equal to -1.
B (output) DOUBLE PRECISION On entry, the destination matrix. The portion corresponding to the defined submatrix are updated.
IB,JB (input) INTEGER On entry,the coordinates of the beginning of the submatrix of B that will be updated. 1 <= IB <= M_B - M + 1,1 <= JB <= N_B - N + 1, Unchanged on exit.
BDESC (input) B description vector (see Notes above) For processors not part of the context of B BDESC[CTXT] must be equal to -1.
CTXT (input) a context englobing at least all processors included in either A context or B context
Memory requirement :
for the processors belonging to grid 0, one buffer of size block 0 and for the processors belonging to grid 1, also one buffer of size block 1.
Created March 1993 by B. Tourancheau (See sccs for modifications).
Modifications by Loic PRYLLI 1995
Definition at line 143 of file pdgemr.c.
1.8.16 
