SUBROUTINE PCELSET( A, IA, JA, DESCA, ALPHA ) *
* -- ScaLAPACK tools routine (version 1.5) --

*     University of Tennessee, Knoxville, Oak Ridge National Laboratory,
*     and University of California, Berkeley.
*     May 1, 1997
*
*     .. Scalar Arguments ..
      INTEGER            IA, JA
      COMPLEX            ALPHA
*     ..
*     .. Array arguments ..
      INTEGER            DESCA( * )
      COMPLEX            A( * )
*     ..

*
* Purpose


*
* PCELSET sets the distributed matrix entry A( IA, JA ) to ALPHA. *
* 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


*
*  A       (local output) COMPLEX pointer into the local memory
*          to an array of dimension (LLD_A,*) containing the local
*          pieces of the distributed matrix A.
*
*  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. *
* ALPHA (local input) COMPLEX
* The scalar alpha.
*


*
*     .. Parameters ..
      INTEGER            BLOCK_CYCLIC_2D, CSRC_, CTXT_, DLEN_, DTYPE_,
     $                   LLD_, MB_, M_, NB_, N_, RSRC_
      PARAMETER          ( BLOCK_CYCLIC_2D = 1, DLEN_ = 9, DTYPE_ = 1,
     $                     CTXT_ = 2, M_ = 3, N_ = 4, MB_ = 5, NB_ = 6,
     $                     RSRC_ = 7, CSRC_ = 8, LLD_ = 9 )
*     ..
*     .. Local Scalars ..
      INTEGER            IACOL, IAROW, IIA, JJA, MYCOL, MYROW, NPCOL,
     $                   NPROW
*     ..
*     .. External Subroutines ..
      EXTERNAL           BLACS_GRIDINFO, INFOG2L
*     ..
*     .. Executable Statements ..
*
*     Get grid parameters.
*
      CALL BLACS_GRIDINFO( DESCA( CTXT_ ), NPROW, NPCOL, MYROW, MYCOL )
*
      CALL INFOG2L( IA, JA, DESCA, NPROW, NPCOL, MYROW, MYCOL, IIA, JJA,
     $              IAROW, IACOL )
*
      IF( MYROW.EQ.IAROW .AND. MYCOL.EQ.IACOL )
     $   A( IIA+(JJA-1)*DESCA( LLD_ ) ) = ALPHA
*
      RETURN
*
*     End of PCELSET
*
      END