PDLASWP - perform a series of row or column interchanges on the distributed
matrix sub( A ) = A(IA:IA+M-1,JA:JA+N-1)
- 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( * )
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
- 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.