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NAME

       PSLASWP  -  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 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
       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 PSLAPIV.

       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) 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.