mirror of https://gitlab.com/QEF/q-e.git
86 lines
2.4 KiB
Fortran
86 lines
2.4 KiB
Fortran
INTEGER FUNCTION NPREROC( N, NB, IPROC, ISRCPROC, NPROCS )
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*
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* -- ScaLAPACK tools routine (version 1.5) --
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* University of Tennessee, Knoxville, Oak Ridge National Laboratory,
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* and University of California, Berkeley.
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* May 1, 1997
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*
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* .. Scalar Arguments ..
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INTEGER IPROC, ISRCPROC, N, NB, NPROCS
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* ..
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*
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* Purpose
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* =======
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*
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* NPREROC computes the Number of PREceeding Rows Or Columns of a
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* distributed matrix that are possessed by processes closer to
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* ISRCPROC than IPROC. Therefore, if ISRCPROC=0 and IPROC=4, then
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* NPREROC returns the number of distributed matrix rows or columns
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* owned by processes 0, 1, 2, and 3.
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*
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* Arguments
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* =========
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*
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* N (global input) INTEGER
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* The number of rows or columns in the distributed matrix.
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*
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* NB (global input) INTEGER
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* Block size, size of the blocks the distributed matrix is
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* split into.
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*
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* IPROC (local intput) INTEGER
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* The coordinate of the process whose preceeding distributed
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* matrix rows or columns are to be determined.
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*
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* ISRCPROC (global input) INTEGER
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* The coordinate of the process that possesses the first
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* row or column of the distributed matrix.
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*
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* NPROCS (global input) INTEGER
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* The total number processes over which the matrix is
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* distributed.
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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INTEGER EXTRABLKS, MYDIST, NBLOCKS
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MOD
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* ..
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* .. Executable Statements ..
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*
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* Figure PROC's distance from source process
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*
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MYDIST = MOD( NPROCS+IPROC-ISRCPROC, NPROCS )
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*
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* Figure the total number of whole NB blocks N is split up into
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*
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NBLOCKS = N / NB
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*
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* Figure the minimum number of rows/cols previous processes could have
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*
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NPREROC = (NBLOCKS/NPROCS) * NB * MYDIST
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*
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* See if there are any extra blocks
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*
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EXTRABLKS = MOD( NBLOCKS, NPROCS )
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*
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* If I have an extra block, all processes in front of me got one too
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*
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IF( MYDIST.LE.EXTRABLKS ) THEN
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NPREROC = NPREROC + NB*MYDIST
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*
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* If I have don't have an extra block, add in extra blocks of
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* preceeding processes and the partial block, if it exists
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*
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ELSE
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NPREROC = NPREROC + EXTRABLKS*NB + MOD( N, NB )
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END IF
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*
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RETURN
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*
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* End of NPREROC
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*
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END
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