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.