NAME
PDLASWP - perform a series of row or column interchanges on the
distributed matrix sub( A ) = A(IA:IA+M-1,JA:JA+N-1)
SYNOPSIS
SUBROUTINE PDLASWP( DIREC, ROWCOL, N, A, IA, JA, DESCA, K1, K2, IPIV )
CHARACTER DIREC, ROWCOL
INTEGER IA, JA, K1, K2, N
INTEGER DESCA( * ), IPIV( * )
DOUBLE PRECISION A( * )
PURPOSE
PDLASWP performs a series of row or column interchanges on the
distributed 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
broadcast 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 PDLAPIV.
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
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) DOUBLE PRECISION 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.