PCLAPV2(3)    ScaLAPACK routine of NEC Numeric Library Collection   PCLAPV2(3)



NAME
       PCLAPV2  -  applie  either  P (permutation matrix indicated by IPIV) or
       inv(  P  )  to  a  M-by-N  distributed  matrix  sub(   A   )   denoting
       A(IA:IA+M-1,JA:JA+N-1), resulting in row or column pivoting

SYNOPSIS
       SUBROUTINE PCLAPV2( DIREC,  ROWCOL,  M,  N, A, IA, JA, DESCA, IPIV, IP,
                           JP, DESCIP )

           CHARACTER       DIREC, ROWCOL

           INTEGER         IA, IP, JA, JP, M, N

           INTEGER         DESCA( * ), DESCIP( * ), IPIV( * )

           COMPLEX         A( * )

PURPOSE
       PCLAPV2 applies either P (permutation matrix indicated by IPIV) or inv(
       P   )   to   a   M-by-N   distributed   matrix   sub(   A   )  denoting
       A(IA:IA+M-1,JA:JA+N-1), resulting in row or column pivoting. The  pivot
       vector  should  be aligned with the distributed matrix A.  For pivoting
       the rows of sub( A ), IPIV should be distributed along a process column
       and  replicated  over all process rows.  Similarly, IPIV should be dis-
       tributed along a process row and replicated over  all  process  columns
       for column pivoting.


       Notes
       =====

       Each  global data object is described by an associated description vec-
       tor.  This vector stores the information required to establish the map-
       ping 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  col-
       umn.
       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) Applies pivots Forward from top of matrix.   Computes
               P  *  sub(  A  ); = 'B' (Backward) Applies pivots Backward from
               bottom of matrix. Computes inv( P ) * sub( A ).

       ROWCOL  (global input) CHARACTER
               Specifies if the rows or columns are to be permuted: = 'R' Rows
               will be permuted, = 'C' Columns will be permuted.

       M       (global input) INTEGER
               The  number  of rows to be operated on, i.e. the number of rows
               of the distributed submatrix sub( A ). M >= 0.

       N       (global input) INTEGER
               The number of columns to be operated on,  i.e.  the  number  of
               columns of the distributed submatrix sub( A ). N >= 0.

       A       (local input/local output) COMPLEX pointer into the
               local  memory  to  an array of dimension (LLD_A, LOCc(JA+N-1)).
               On entry, this local array contains the  local  pieces  of  the
               distributed  matrix sub( A ) to which the row or columns inter-
               changes will be applied. On exit, this array contains the local
               pieces of 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.

       IPIV    (input) INTEGER array, dimension >= LOCr(M_A)+MB_A if
               ROWCOL  = 'R', LOCc(N_A)+NB_A otherwise. It contains the pivot-
               ing information. IPIV(i) is the global row (column), local  row
               (column)  i  was  swapped with.  The last piece of the array of
               size MB_A (resp. NB_A) is used as workspace. IPIV  is  tied  to
               the distributed matrix A.

       IP      (global input) INTEGER
               IPIV's  global  row index, which points to the beginning of the
               submatrix which is to be operated on.

       JP      (global input) INTEGER
               IPIV's global column index, which points to  the  beginning  of
               the submatrix which is to be operated on.

       DESCIP  (global and local input) INTEGER array of dimension 8
               The array descriptor for the distributed matrix IPIV.



ScaLAPACK routine               31 October 2017                     PCLAPV2(3)