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.TH HPL_reduce 3 "September 10, 2008" "HPL 2.0" "HPL Library Functions"
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.SH NAME
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HPL_reduce \- Reduce operation.
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.SH SYNOPSIS
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\fB\&#include "hpl.h"\fR
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\fB\&int\fR
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\fB\&HPL_reduce(\fR
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\fB\&void *\fR
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\fI\&BUFFER\fR,
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\fB\&const int\fR
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\fI\&COUNT\fR,
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\fB\&const HPL_T_TYPE\fR
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\fI\&DTYPE\fR,
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\fB\&const HPL_T_OP \fR
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\fI\&OP\fR,
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\fB\&const int\fR
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\fI\&ROOT\fR,
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\fB\&MPI_Comm\fR
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\fI\&COMM\fR
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\fB\&);\fR
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.SH DESCRIPTION
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\fB\&HPL_reduce\fR
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performs a global reduce operation across all processes of
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a group.  Note that the input buffer is  used as workarray and in all
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processes but the accumulating process corrupting the original data.
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.SH ARGUMENTS
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.TP 8
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BUFFER  (local input/output)    void *
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On entry,  BUFFER  points to  the  buffer to be  reduced.  On
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exit,  and  in process of rank  ROOT  this array contains the
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reduced data.  This  buffer  is also used as workspace during
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the operation in the other processes of the group.
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.TP 8
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COUNT   (global input)          const int
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On entry,  COUNT  indicates the number of entries in  BUFFER.
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COUNT must be at least zero.
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.TP 8
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DTYPE   (global input)          const HPL_T_TYPE
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On entry,  DTYPE  specifies the type of the buffers operands.
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.TP 8
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OP      (global input)          const HPL_T_OP
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On entry, OP is a pointer to the local combine function.
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.TP 8
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ROOT    (global input)          const int
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On entry, ROOT is the coordinate of the accumulating process.
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.TP 8
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COMM    (global/local input)    MPI_Comm
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The MPI communicator identifying the process collection.
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.SH SEE ALSO
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.BR HPL_broadcast \ (3),
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.BR HPL_all_reduce \ (3),
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.BR HPL_barrier \ (3),
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.BR HPL_min \ (3),
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.BR HPL_max \ (3),
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.BR HPL_sum \ (3).