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lammps/lib/kokkos/example/tutorial/02_simple_reduce/simple_reduce.cpp
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/*
//@HEADER
// ************************************************************************
//
// Kokkos v. 2.0
// Copyright (2014) Sandia Corporation
//
// Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation,
// the U.S. Government retains certain rights in this software.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// 3. Neither the name of the Corporation nor the names of the
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY SANDIA CORPORATION "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SANDIA CORPORATION OR THE
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Questions? Contact H. Carter Edwards (hcedwar@sandia.gov)
//
// ************************************************************************
//@HEADER
*/
#include <Kokkos_Core.hpp>
#include <cstdio>
//
// First reduction (parallel_reduce) example:
// 1. Start up Kokkos
// 2. Execute a parallel_reduce loop in the default execution space,
// using a functor to define the loop body
// 3. Shut down Kokkos
//
// Compare this example to 02_simple_reduce_lambda, which uses a C++11
// lambda to define the loop body of the parallel_reduce.
//
// Reduction functor for computing the sum of squares.
//
// More advanced reduction examples will show how to control the
// reduction's "join" operator. If the join operator is not provided,
// it defaults to binary operator+ (adding numbers together).
struct squaresum {
// Specify the type of the reduction value with a "value_type"
// typedef. In this case, the reduction value has type int.
typedef int value_type;
// The reduction functor's operator() looks a little different than
// the parallel_for functor's operator(). For the reduction, we
// pass in both the loop index i, and the intermediate reduction
// value lsum. The latter MUST be passed in by nonconst reference.
// (If the reduction type is an array like int[], indicating an
// array reduction result, then the second argument is just int[].)
KOKKOS_INLINE_FUNCTION
void operator () (const int i, int& lsum) const {
lsum += i*i; // compute the sum of squares
}
};
int main (int argc, char* argv[]) {
Kokkos::initialize (argc, argv);
const int n = 10;
// Compute the sum of squares of integers from 0 to n-1, in
// parallel, using Kokkos.
int sum = 0;
Kokkos::parallel_reduce (n, squaresum (), sum);
printf ("Sum of squares of integers from 0 to %i, "
"computed in parallel, is %i\n", n - 1, sum);
// Compare to a sequential loop.
int seqSum = 0;
for (int i = 0; i < n; ++i) {
seqSum += i*i;
}
printf ("Sum of squares of integers from 0 to %i, "
"computed sequentially, is %i\n", n - 1, seqSum);
Kokkos::finalize ();
return (sum == seqSum) ? 0 : -1;
}
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