# p?laswp

Performs a series of row interchanges on a general rectangular matrix.

## Syntax

call pslaswp(direc, rowcol, n, a, ia, ja, desca, k1, k2, ipiv)

call pdlaswp(direc, rowcol, n, a, ia, ja, desca, k1, k2, ipiv)

call pclaswp(direc, rowcol, n, a, ia, ja, desca, k1, k2, ipiv)

call pzlaswp(direc, rowcol, n, a, ia, ja, desca, k1, k2, ipiv)

## Description

This routine performs a series of row or column interchanges on the distributed matrix `sub(A)=A(ia:ia+n-1, ja:ja+n-1)`. One interchange is initiated for each of rows or columns k1 through 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 p?lapiv.

## Input Parameters

direc

  (global) CHARACTER.

  Specifies in which order the permutation is applied:

  = 'F' - forward,

  = 'B' - backward.

rowcol

  (global) CHARACTER.

  Specifies if the rows or columns are permuted:

  = 'R' - rows,

  = 'C' - columns.

n

  (global) 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)

  REAL for pslaswp

  DOUBLE PRECISION for pdlaswp

  COMPLEX for pclaswp

  COMPLEX*16 for pzlaswp.

  Pointer into the local memory to an array of DIMENSION (lld_a, *). On entry, this array contains the local pieces of the distributed matrix to which the row/columns interchanges will be applied.

ia

  (global) INTEGER.

  The row index in the global array A indicating the first row of sub(A).

ja

  (global) INTEGER.

  The column index in the global array A indicating the first column of sub(A).

desca

  (global and local) INTEGER array of DIMENSION (dlen_).

  The array descriptor for the distributed matrix A.

k1

  (global) INTEGER.

  The first element of ipiv for which a row or column interchange will be done.

k2

  (global) INTEGER.

  The last element of ipiv for which a row or column interchange will be done.

ipiv

  (local)

  INTEGER. Array, DIMENSION `LOCr(m_a)+mb_a` for row pivoting and `LOCr(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.

## Output Parameters

A

  (local)

  REAL for pslaswp

  DOUBLE PRECISION for pdlaswp

  COMPLEX for pclaswp

  COMPLEX*16 for pzlaswp.

  On exit, the permuted distributed matrix.

Parent topic: Auxiliary Routines