SUBROUTINE INFOG2L( GRINDX, GCINDX, DESC, NPROW, NPCOL, MYROW,
     $                    MYCOL, LRINDX, LCINDX, RSRC, CSRC )

*
* -- 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            CSRC, GCINDX, GRINDX, LRINDX, LCINDX, MYCOL,
     $                   MYROW, NPCOL, NPROW, RSRC
*     ..
*     .. Array Arguments ..
      INTEGER            DESC( * )
*     ..

*
* Purpose


*
*  INFOG2L computes the starting local indexes LRINDX, LCINDX corres-
*  ponding to the distributed submatrix starting globally at the entry
*  pointed by GRINDX, GCINDX. This routine returns the coordinates in
*  the grid of the process owning the matrix entry of global indexes
*  GRINDX, GCINDX, namely RSRC and CSRC.
*
* 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


*
* GRINDX (global input) INTEGER
* The global row starting index of the submatrix. *
* GCINDX (global input) INTEGER
* The global column starting index of the submatrix. * * DESC (input) INTEGER array of dimension DLEN_. * The array descriptor for the underlying distributed matrix. * * NPROW (global input) INTEGER * The total number of process rows over which the distributed * matrix is distributed. * * NPCOL (global input) INTEGER * The total number of process columns over which the * distributed matrix is distributed. * * MYROW (local input) INTEGER * The row coordinate of the process calling this routine. * * MYCOL (local input) INTEGER * The column coordinate of the process calling this routine.

*
* LRINDX (local output) INTEGER
* The local rows starting index of the submatrix. *
* LCINDX (local output) INTEGER
* The local columns starting index of the submatrix. * * RSRC (global output) INTEGER * The row coordinate of the process that possesses the first * row and column of the submatrix. * * CSRC (global output) INTEGER * The column coordinate of the process that possesses the * first row and column of the submatrix.

*


*
*     .. 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            CBLK, GCCPY, GRCPY, RBLK
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          MOD
*     ..
*     .. Executable Statements ..
*
      GRCPY = GRINDX-1
      GCCPY = GCINDX-1
*
      RBLK = GRCPY / DESC(MB_)
      CBLK = GCCPY / DESC(NB_)
      RSRC = MOD( RBLK + DESC(RSRC_), NPROW )
      CSRC = MOD( CBLK + DESC(CSRC_), NPCOL )
*
      LRINDX = ( RBLK / NPROW + 1 ) * DESC(MB_) + 1
      LCINDX = ( CBLK / NPCOL + 1 ) * DESC(NB_) + 1
*
      IF( MOD( MYROW+NPROW-DESC(RSRC_), NPROW ) .GE.
     $    MOD( RBLK, NPROW ) ) THEN
         IF( MYROW.EQ.RSRC )
     $      LRINDX = LRINDX + MOD( GRCPY, DESC(MB_) )
         LRINDX = LRINDX - DESC(MB_)
      END IF
*
      IF( MOD( MYCOL+NPCOL-DESC(CSRC_), NPCOL ) .GE.
     $    MOD( CBLK, NPCOL ) ) THEN
         IF( MYCOL.EQ.CSRC )
     $      LCINDX = LCINDX + MOD( GCCPY, DESC(NB_) )
         LCINDX = LCINDX - DESC(NB_)
      END IF
*
      RETURN
*
*     End of INFOG2L
*
      END