PSLASWP(3) ScaLAPACK routine of NEC Numeric Library Collection PSLASWP(3)
NAME
PSLASWP - perform a series of row or column interchanges on the dis-
tributed matrix sub( A ) = A(IA:IA+M-1,JA:JA+N-1)
SYNOPSIS
SUBROUTINE PSLASWP( DIREC, ROWCOL, N, A, IA, JA, DESCA, K1, K2, IPIV )
CHARACTER DIREC, ROWCOL
INTEGER IA, JA, K1, K2, N
INTEGER DESCA( * ), IPIV( * )
REAL A( * )
PURPOSE
PSLASWP performs a series of row or column interchanges on the dis-
tributed matrix sub( A ) = A(IA:IA+M-1,JA:JA+N-1). One interchange is
initiated for each of rows or columns K1 trough K2 of sub( A ). This
routine assumes that the pivoting information has already been broad-
cast along the process row or column.
Also note that this routine will only work for K1-K2 being in the same
MB (or NB) block. If you want to pivot a full matrix, use PSLAPIV.
Notes
=====
Each global data object is described by an associated description vec-
tor. This vector stores the information required to establish the map-
ping 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
DIREC (global input) CHARACTER
Specifies in which order the permutation is applied: = 'F'
(Forward) = 'B' (Backward)
ROWCOL (global input) CHARACTER
Specifies if the rows or columns are permuted: = 'R' (Rows) =
'C' (Columns)
N (global input) INTEGER
If ROWCOL = 'R', the length of the rows of the distributed
matrix A(*,JA:JA+N-1) to be permuted; If ROWCOL = 'C', the
length of the columns of the distributed matrix A(IA:IA+N-1,*)
to be permuted.
A (local input/local output) REAL pointer into the
local memory to an array of dimension (LLD_A, * ). On entry,
this array contains the local pieces of the distri- buted
matrix to which the row/columns interchanges will be applied.
On exit the permuted distributed matrix.
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.
K1 (global input) INTEGER
The first element of IPIV for which a row or column inter-
change will be done.
K2 (global input) INTEGER
The last element of IPIV for which a row or column inter-
change will be done.
IPIV (local input) INTEGER array, dimension LOCr(M_A)+MB_A for
row pivoting and LOCc(N_A)+NB_A for column pivoting. This
array is tied to the matrix A, IPIV(K) = L implies rows (or
columns) K and L are to be interchanged.
ScaLAPACK routine 31 October 2017 PSLASWP(3)