PSLARED2D(3)             MathKeisan ScaLAPACK routine             PSLARED2D(3)



NAME
       PSLARED2D  -  redistribute a 1D array  It assumes that the input array,
       BYROW, is distributed across columns and that all process rows  contain
       the same copy of BYROW

SYNOPSIS
       SUBROUTINE PSLARED2D( N, IA, JA, DESC, BYROW, BYALL, WORK, LWORK )

           INTEGER           IA, JA, LWORK, N

           INTEGER           DESC( * )

           REAL              BYALL( * ), BYROW( * ), WORK( LWORK )

PURPOSE
       PSLARED2D  redistributes  a  1D  array It assumes that the input array,
       BYROW, is distributed across columns and that all process rows  contain
       the  same  copy of BYROW. The output array, BYALL, will be identical on
       all processes and will contain the entire array.

       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
       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
       NP = Number of local rows in BYROW()

       N       (global input) INTEGER
               The number of elements to be redistributed.  N >= 0.

       IA      (global input) INTEGER
               IA must be equal to 1

       JA      (global input) INTEGER
               JA must be equal to 1

       DESC    (global/local input) INTEGER Array of dimension DLEN_
               A 2D array descriptor, which describes BYROW

       BYROW   (local input) distributed block cyclic REAL            array
               global  dimension  (N), local dimension NP BYCOL is distributed
               across the process columns All process rows are assumed to con-
               tain the same value

       BYALL   (global output) REAL            global dimension( N )
               local  dimension  (N)  BYALL  is exactly duplicated on all pro-
               cesses It contains the same values as BYCOL, but it  is  repli-
               cated across all processes rather than being distributed

               BYALL(i)  =  BYCOL(  NUMROC(i,NB,MYROW,0,NPROW  )  on the procs
               whose MYROW == mod((i-1)/NB,NPROW)

       WORK    (local workspace) REAL            dimension (LWORK)
               Used to hold the buffers sent from one process to another

       LWORK   (local input) INTEGER size of WORK array LWORK >=
               LWORK >= NUMROC(N, DESC( NB_ ), 0, 0, NPCOL)



ScaLAPACK version 1.7           13 August 2001                    PSLARED2D(3)