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//                        Kokkos v. 2.0
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//
// First Kokkos::View (multidimensional array) example:
//   1. Start up Kokkos
//   2. Allocate a Kokkos::View
//   3. Execute a parallel_for and a parallel_reduce over that View's data
//   4. Shut down Kokkos
//
// Compare this example to 03_simple_view, which uses functors to
// define the loop bodies of the parallel_for and parallel_reduce.
//

#include <Kokkos_Core.hpp>
#include <cstdio>

// A Kokkos::View is an array of zero or more dimensions.  The number
// of dimensions is specified at compile time, as part of the type of
// the View.  This array has two dimensions.  The first one
// (represented by the asterisk) is a run-time dimension, and the
// second (represented by [3]) is a compile-time dimension.  Thus,
// this View type is an N x 3 array of type double, where N is
// specified at run time in the View's constructor.
//
// The first dimension of the View is the dimension over which it is
// efficient for Kokkos to parallelize.
typedef Kokkos::View<double*[3]> view_type;

int main (int argc, char* argv[]) {
  Kokkos::initialize (argc, argv);

  // Allocate the View.  The first dimension is a run-time parameter
  // N.  We set N = 10 here.  The second dimension is a compile-time
  // parameter, 3.  We don't specify it here because we already set it
  // by declaring the type of the View.
  //
  // Views get initialized to zero by default.  This happens in
  // parallel, using the View's memory space's default execution
  // space.  Parallel initialization ensures first-touch allocation.
  // There is a way to shut off default initialization.
  //
  // You may NOT allocate a View inside of a parallel_{for, reduce,
  // scan}.  Treat View allocation as a "thread collective."
  //
  // The string "A" is just the label; it only matters for debugging.
  // Different Views may have the same label.
  view_type a ("A", 10);

  // Fill the View with some data.  The parallel_for loop will iterate
  // over the View's first dimension N.
  //
  // Note that the View is passed by value into the lambda.  The macro
  // KOKKOS_LAMBDA includes the "capture by value" clause [=].  This
  // tells the lambda to "capture all variables in the enclosing scope
  // by value."  Views have "view semantics"; they behave like
  // pointers, not like std::vector.  Passing them by value does a
  // shallow copy.  A deep copy never happens unless you explicitly
  // ask for one.
  Kokkos::parallel_for (10, KOKKOS_LAMBDA (const int i) {
    // Acesss the View just like a Fortran array.  The layout depends
    // on the View's memory space, so don't rely on the View's
    // physical memory layout unless you know what you're doing.
    a(i,0) = 1.0*i;
    a(i,1) = 1.0*i*i;
    a(i,2) = 1.0*i*i*i;
  });
  // Reduction functor that reads the View given to its constructor.
  double sum = 0;
  Kokkos::parallel_reduce (10, KOKKOS_LAMBDA (const int i, double& lsum) {
    lsum += a(i,0)*a(i,1)/(a(i,2)+0.1);
  }, sum);
  printf ("Result: %f\n", sum);
  Kokkos::finalize ();
}

