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



NAME
       PSLASET  -  initialize  an  M-by-N distributed matrix sub( A ) denoting
       A(IA:IA+M-1,JA:JA+N-1) to BETA on the diagonal and ALPHA on the  offdi-
       agonals

SYNOPSIS
       SUBROUTINE PSLASET( UPLO, M, N, ALPHA, BETA, A, IA, JA, DESCA )

           CHARACTER       UPLO

           INTEGER         IA, JA, M, N

           REAL            ALPHA, BETA

           INTEGER         DESCA( * )

           REAL            A( * )

PURPOSE
       PSLASET  initializes  an  M-by-N  distributed  matrix sub( A ) denoting
       A(IA:IA+M-1,JA:JA+N-1) to BETA on the diagonal and ALPHA on the  offdi-
       agonals.

       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
       UPLO    (global input) CHARACTER
               Specifies  the  part  of  the distributed matrix sub( A ) to be
               set:
               = 'U':      Upper triangular part is set;  the  strictly  lower
               triangular  part  of sub( A ) is not changed; = 'L':      Lower
               triangular part is set; the strictly upper triangular  part  of
               sub( A ) is not changed; Otherwise:  All of the matrix sub( A )
               is set.

       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.

       ALPHA   (global input) REAL
               The constant to which the offdiagonal elements are to be set.

       BETA    (global input) REAL
               The constant to which the diagonal elements are to be set.

       A       (local output) REAL pointer into the local memory
               to an array of dimension (LLD_A,LOCc(JA+N-1)).  This array con-
               tains the local pieces of the distributed matrix sub( A ) to be
               set.  On exit, the leading M-by-N submatrix sub( A ) is set  as
               follows:

               if UPLO = 'U', A(IA+i-1,JA+j-1) = ALPHA, 1<=i<=j-1, 1<=j<=N, if
               UPLO = 'L', A(IA+i-1,JA+j-1) = ALPHA, j+1<=i<=M, 1<=j<=N,  oth-
               erwise,       A(IA+i-1,JA+j-1)   =   ALPHA,  1<=i<=M,  1<=j<=N,
               IA+i.NE.JA+j, and,  for  all  UPLO,  A(IA+i-1,JA+i-1)  =  BETA,
               1<=i<=min(M,N).

       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.



ScaLAPACK routine               31 October 2017                     PSLASET(3)