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NAME

       shmem_comp4_prod_to_all(3),   shmem_comp8_prod_to_all(3),   shmem_complexd_prod_to_all(3),
       shmem_complexf_prod_to_all(3),  shmem_double_prod_to_all(3),   shmem_float_prod_to_all(3),
       shmem_int_prod_to_all(3),       shmem_int4_prod_to_all(3),      shmem_int8_prod_to_all(3),
       shmem_long_prod_to_all(3), shmem_longdouble_prod_to_all(3), shmem_longlong_prod_to_all(3),
       shmem_real8_prod_to_all(3),    shmem_real16_prod_to_all(3),    shmem_real4_prod_to_all(3),
       shmem_short_prod_to_all(3) - Performs a product  reduction  across  a  set  of  processing
       elements (PEs)

SYNOPSIS

       C or C++:
       #include <mpp/shmem.h>

       void shmem_complexd_prod_to_all(double complex *target,
         const double complex *source, int nreduce, int PE_start,
         int logPE_stride, int PE_size, double complex *pWrk,
         long *pSync);

       void shmem_complexf_prod_to_all(float complex *target,
         const float complex *source, int nreduce, int PE_start,
         int logPE_stride, int PE_size, float complex *pWrk,
         long *pSync);

       void shmem_double_prod_to_all(double *target, const double *source,
         int nreduce, int PE_start, int logPE_stride, int PE_size,
         double *pWrk, long *pSync);

       void shmem_float_prod_to_all(float *target, const float *source,
         int nreduce, int PE_start, int logPE_stride, int PE_size,
         float *pWrk, long *pSync);

       void shmem_int_prod_to_all(int *target, const int *source,
         int nreduce, int PE_start, int logPE_stride, int PE_size,
         int *pWrk, long *pSync);

       void shmem_long_prod_to_all(long *target, const long *source,
         int nreduce, int PE_start, int logPE_stride, int PE_size,
         long *pWrk, long *pSync);

       void shmem_longdouble_prod_to_all(long double *target,
         const long double *source, int nreduce, int PE_start,
         int logPE_stride, int PE_size, long double *pWrk,
         long *pSync);

       void shmem_longlong_prod_to_all(long long *target,
         const long long *source, int nreduce, int PE_start,
         int logPE_stride, int PE_size, long long *pWrk,
         long *pSync);

       void shmem_short_prod_to_all(short *target, const short *source,
         int nreduce, int PE_start, int logPE_stride, int PE_size,
         short *pWrk, long *pSync);

       Fortran:
       INCLUDE "mpp/shmem.fh"

       INTEGER pSync(SHMEM_REDUCE_SYNC_SIZE)
       INTEGER nreduce, PE_start, logPE_stride, PE_size

       CALL SHMEM_COMP4_PROD_TO_ALL(target, source, nreduce, PE_start,
       & logPE_stride, PE_size, pWrk, pSync)

       CALL SHMEM_COMP8_PROD_TO_ALL(target, source, nreduce, PE_start,
       & logPE_stride, PE_size, pWrk, pSync)

       CALL SHMEM_INT4_PROD_TO_ALL(target, source, nreduce, PE_start,
       & logPE_stride, PE_size, pWrk, pSync)

       CALL SHMEM_INT8_PROD_TO_ALL(target, source, nreduce, PE_start,
       & logPE_stride, PE_size, pWrk, pSync)

       CALL SHMEM_REAL4_PROD_TO_ALL(target, source, nreduce, PE_start,
       & logPE_stride, PE_size, pWrk, pSync)

       CALL SHMEM_REAL8_PROD_TO_ALL(target, source, nreduce, PE_start,
       & logPE_stride, PE_size, pWrk, pSync)

       CALL SHMEM_REAL16_PROD_TO_ALL(target, source, nreduce, PE_start,
       & logPE_stride, PE_size, pWrk, pSync)

DESCRIPTION

       The  shared  memory  (SHMEM)  reduction  routines  compute  one  or more reductions across
       symmetric arrays on multiple virtual PEs.  A  reduction  performs  an  associative  binary
       operation  across  a  set  of  values.  For  a list of other SHMEM reduction routines, see
       intro_shmem(3).

       As with all SHMEM collective routines, each of these routines assumes that only PEs in the
       active  set  call  the  routine.  If  a  PE not in the active set calls a SHMEM collective
       routine, undefined behavior results.

       The nreduce argument determines the number of separate reductions to perform.  The  source
       array on all PEs in the active set provides one element for each reduction. The results of
       the reductions are placed in the target array on all PEs in the active set. The active set
       is defined by the PE_start, logPE_stride, PE_size triplet.

       The  source  and  target  arrays  may  be  the same array, but they may not be overlapping
       arrays.

       The arguments are as follows:

       target A symmetric array of  length  nreduce  elements  to  receive  the  results  of  the
              reduction  operations.  The  data  type  of  target  varies with the version of the
              reduction routine being called and the language  used.  When  calling  from  C/C++,
              refer to the SYNOPSIS section for data type information. When calling from Fortran,
              the target data types are as follows:

              shmem_comp4_prod_to_all: Complex, with an element size equal to two
                     4-byte real values.

              shmem_comp8_prod_to_all: Complex, with an element size equal to two
                     8-byte real values.

              shmem_int4_prod_to_all: Integer, with an element size of 4 bytes

              shmem_int8_prod_to_all: Integer, with an element size of 8 bytes

              shmem_real4_prod_to_all: Real, with an element size of 4 bytes

              shmem_real8_prod_to_all: Real, with an element size of 8 bytes

              shmem_real16_prod_to_all: Real, with an element size of 16 bytes

       source A symmetric array, of length nreduce elements, that contains one element  for  each
              separate  reduction  operation. The source argument must have the same data type as
              target.

       nreduce
              The number of elements in the target and source arrays. nreduce  must  be  of  type
              integer. If you are using Fortran, it must be a default integer value.

       PE_start
              The  lowest  virtual  PE  number of the active set of PEs. PE_start must be of type
              integer. If you are using Fortran, it must be a default integer value.

       logPE_stride
              The log (base 2) of the stride between consecutive virtual PE numbers in the active
              set.  logPE_stride  must be of type integer. If you are using Fortran, it must be a
              default integer value.

       PE_size
              The number of PEs in the active set. PE_size must be of type integer.  If  you  are
              using Fortran, it must be a default integer value.

       pWrk   A  symmetric  work array. The pWrk argument must have the same data type as target.
              In  C/C++,  this  contains  max(nreduce/2  +   1,   _SHMEM_REDUCE_MIN_WRKDATA_SIZE)
              elements.      In     Fortran,     this     contains     max(nreduce/2     +     1,
              SHMEM_REDUCE_MIN_WRKDATA_SIZE) elements.

       pSync  A  symmetric  work  array.  In  C/C++,   pSync   is   of   type   long   and   size
              _SHMEM_REDUCE_SYNC_SIZE.   In   Fortran,   pSync   is  of  type  integer  and  size
              SHMEM_REDUCE_SYNC_SIZE. If you are using Fortran, it  must  be  a  default  integer
              value.   Before any of the PEs in the active set enter the reduction routine, every
              element of this array must be initialized  with  the  value  _SHMEM_SYNC_VALUE  (in
              C/C++) or SHMEM_SYNC_VALUE (in Fortran).

       The  values of arguments nreduce, PE_start, logPE_stride, and PE_size must be equal on all
       PEs in the active set. The same target and source arrays, and the same pWrk and pSync work
       arrays,  must  be  passed  to  all  PEs in the active set. Before any PE calls a reduction
       routine, you must ensure that  the  following  conditions  exist  (synchronization  via  a
       barrier or some other method is often needed to ensure this): The pWrk and pSync arrays on
       all PEs in the active set are not still in use from a prior call  to  a  collective  SHMEM
       routine.  The  target array on all PEs in the active set is ready to accept the results of
       the reduction.

       Upon return from a reduction routine, the following are true for the local PE: The  target
       array is updated. The values in the pSync array are restored to the original values.

NOTES

       The  terms  collective,  symmetric,  and cache aligned are defined in intro_shmem(3).  All
       SHMEM reduction routines reset the values in pSync before they  return,  so  a  particular
       pSync buffer need only be initialized the first time it is used.

       You  must  ensure  that  the  pSync array is not being updated on any PE in the active set
       while any of the PEs participate in processing of a SHMEM reduction routine. Be careful of
       the  following  situations:  If  the  pSync array is initialized at run time, some type of
       synchronization is needed to ensure that all PEs in the working set have initialized pSync
       before  any  of  them enter a SHMEM routine called with the pSync synchronization array. A
       pSync or pWrk array can be reused in a subsequent reduction routine call only if  none  of
       the  PEs  in  the active set are still processing a prior reduction routine call that used
       the same pSync or pWrk arrays. In general, this can be assured only by doing some type  of
       synchronization.  However, in the special case of reduction routines being called with the
       same active set, you can allocate two pSync and pWrk arrays and alternate between them  on
       successive calls.

EXAMPLES

       Example  1:  This  Fortran  example  statically  initializes the pSync array and finds the
       product of the real variable FOO across all the even PEs.
       INCLUDE "mpp/shmem.fh"

       INTEGER PSYNC(SHMEM_REDUCE_SYNC_SIZE)
       DATA PSYNC /SHMEM_REDUCE_SYNC_SIZE*SHMEM_SYNC_VALUE/
       PARAMETER (NR=1)
       REAL FOO, FOOPROD, PWRK(MAX(NR/2+1,SHMEM_REDUCE_MIN_WRKDATA_SIZE))
       COMMON /COM/ FOO, FOOPROD, PWRK
       INTRINSIC MY_PE

       IF ( MOD(MY_PE(),2) .EQ. 0) THEN
         CALL SHMEM_COMP8_PROD_TO_ALL(FOOPROD, FOO, NR, 0, 1, N$PES/2,
         & PWRK, PSYNC)
         PRINT *, 'Result on PE ', MY_PE(), ' is ', FOOPROD
       ENDIF

       Example 2: Consider the following C/C++ call:
       shmem_short_prod_to_all(target, source, 3, 0, 0, 8, pwrk, psync);

       The preceding call is more efficient, but semantically equivalent to, the  combination  of
       the following calls:
       shmem_short_prod_to_all(&(target[0]), &(source[0]), 1, 0, 0, 8,
         pwrk1, psync1);
       shmem_short_prod_to_all(&(target[1]), &(source[1]), 1, 0, 0, 8,
         pwrk2, psync2);
       shmem_short_prod_to_all(&(target[2]), &(source[2]), 1, 0, 0, 8,
         pwrk1, psync1);

       Note   that   two  sets  of  pWrk  and  pSync  arrays  are  used  alternately  because  no
       synchronization is done between calls.

SEE ALSO

       intro_shmem(3)