Add concepts exercise

Exercises/concepts/Begin/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.22)
+project(KokkosTutorialConcepts)
+include(../../common.cmake)
+
+add_executable(concepts concepts.cpp)
+target_link_libraries(concepts Kokkos::kokkos)
+

Exercises/concepts/Begin/concepts.cpp

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+//@HEADER
+// ************************************************************************
+//
+//                        Kokkos v. 4.0
+//       Copyright (2022) National Technology & Engineering
+//               Solutions of Sandia, LLC (NTESS).
+//
+// Under the terms of Contract DE-NA0003525 with NTESS,
+// the U.S. Government retains certain rights in this software.
+//
+// Part of Kokkos, under the Apache License v2.0 with LLVM Exceptions.
+// See https://kokkos.org/LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//@HEADER
+
+#include <limits>
+#include <cmath>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+
+
+#include <Kokkos_Core.hpp>
+
+template<class V>
+concept AnyView = Kokkos::is_view_v<V>;
+
+void checkSizes( int &N, int &M, int &S, int &nrepeat );
+
+// EXERCISE 1: use AnyView and Kokkos::ExecutionSpace concepts for the functions
+// EXERCISE 2: rename init_vector and init_matrix to init_view, and use constraints
+//             (requires clause) to distinguish the overloads
+// EXERCISE 3: Can you do the init_view version as a single function with if constexpr?
+//             What is the downside of that?
+template<class Exec, class Vector>
+void init_vector(Exec exec, Vector x, typename Vector::element_type val) {
+  Kokkos::parallel_for("init_vector", Kokkos::RangePolicy(exec, 0, x.extent_int(0)),
+    KOKKOS_LAMBDA(int i) { x(i) = val; });
+}
+
+template<class Exec, class Matrix>
+void init_matrix(Exec exec, Matrix A, typename Matrix::element_type val) {
+  Kokkos::parallel_for("init_vector",
+    Kokkos::MDRangePolicy<Kokkos::Rank<2>, Exec>(exec, {0,0}, {A.extent_int(0), A.extent_int(1)}),
+    KOKKOS_LAMBDA(int i, int j) { A(i,j) = val; });
+}
+
+// EXERCISE: constrain the function to Views that have arithmetic types as
+//           element types (using requires clause, together with the AnyView concept)
+// EXERCISE: Can you write a Matrix and Vector concept instead?
+// EXERCISE: where and how should you check at compiler time that compile time
+//           extents match where appropriate (instead of just runtime lengths)
+//           Remember static_extent(r) == Kokkos::dynamic_extent for dynamic extents
+template<class Exec, class Matrix, class VectorX, class VectorY>
+double run_code(Exec exec, Matrix A, VectorX x, VectorY y) {  
+  double result;
+  int N = A.extent(0);
+  int M = A.extent(1);
+  if(x.extent(0) != M) Kokkos::abort("X length mismatches number of columns in A");
+  if(y.extent(0) != N) Kokkos::abort("Y length mismatches number of rows in A");
+  Kokkos::parallel_reduce( "yAx", Kokkos::RangePolicy(exec, 0, N),
+    KOKKOS_LAMBDA ( int j, double &update ) {
+      double temp2 = 0;
+
+      for ( int i = 0; i < M; ++i ) {
+        temp2 += A( j, i ) * x( i );
+      }
+
+      update += y( j ) * temp2;
+    }, result );
+  return result;
+}
+
+int main( int argc, char* argv[] )
+{
+  int N = -1;         // number of rows 2^12
+  int M = -1;         // number of columns 2^10
+  int S = -1;         // total size 2^22
+  int nrepeat = 100;  // number of repeats of the test
+
+  // Read command line arguments.
+  for ( int i = 0; i < argc; i++ ) {
+    if ( ( strcmp( argv[ i ], "-N" ) == 0 ) || ( strcmp( argv[ i ], "-Rows" ) == 0 ) ) {
+      N = pow( 2, atoi( argv[ ++i ] ) );
+      printf( "  User N is %d\n", N );
+    }
+    else if ( ( strcmp( argv[ i ], "-M" ) == 0 ) || ( strcmp( argv[ i ], "-Columns" ) == 0 ) ) {
+      M = pow( 2, atof( argv[ ++i ] ) );
+      printf( "  User M is %d\n", M );
+    }
+    else if ( ( strcmp( argv[ i ], "-S" ) == 0 ) || ( strcmp( argv[ i ], "-Size" ) == 0 ) ) {
+      S = pow( 2, atof( argv[ ++i ] ) );
+      printf( "  User S is %d\n", S );
+    }
+    else if ( strcmp( argv[ i ], "-nrepeat" ) == 0 ) {
+      nrepeat = atoi( argv[ ++i ] );
+    }
+    else if ( ( strcmp( argv[ i ], "-h" ) == 0 ) || ( strcmp( argv[ i ], "-help" ) == 0 ) ) {
+      printf( "  y^T*A*x Options:\n" );
+      printf( "  -Rows (-N) <int>:      exponent num, determines number of rows 2^num (default: 2^12 = 4096)\n" );
+      printf( "  -Columns (-M) <int>:   exponent num, determines number of columns 2^num (default: 2^10 = 1024)\n" );
+      printf( "  -Size (-S) <int>:      exponent num, determines total matrix size 2^num (default: 2^22 = 4096*1024 )\n" );
+      printf( "  -nrepeat <int>:        number of repetitions (default: 100)\n" );
+      printf( "  -help (-h):            print this message\n\n" );
+      exit( 1 );
+    }
+  }
+
+  // Check sizes.
+  checkSizes( N, M, S, nrepeat );
+
+  Kokkos::initialize( argc, argv );
+  {
+
+  // Allocate y, x vectors and Matrix A on device.
+  using ViewVectorType = Kokkos::View<double*, Kokkos::SharedSpace>;
+  using ViewMatrixType = Kokkos::View<double**, Kokkos::SharedSpace>;
+  ViewVectorType y( "y", N );
+  ViewVectorType x( "x", M );
+  ViewMatrixType A( "A", N, M );
+
+  auto exec = Kokkos::DefaultExecutionSpace();
+
+  // Initialize y vector on host.
+  init_vector(exec, y, 1);
+
+  // Initialize x vector on host.
+  init_vector(exec, x, 1);
+
+  // Initialize A matrix on host, note 2D indexing.
+  init_matrix(exec, A, 1);
+  Kokkos::fence();
+
+  // EXERCISE: Check error message when using the wrong
+  // function call here before and after introducing concepts
+  // init_vector(exec, A, 1);
+  // init_vector(A, exec, 1);
+
+  // Timer products.
+  Kokkos::Timer timer;
+
+  for ( int repeat = 0; repeat < nrepeat; repeat++ ) {
+    // Application: <y,Ax> = y^T*A*x
+    double result = run_code(exec, A, x, y);
+
+    // Output result.
+    if ( repeat == ( nrepeat - 1 ) ) {
+      printf( "  Computed result for %d x %d is %lf\n", N, M, result );
+    }
+
+    const double solution = (double) N * (double) M;
+
+    if ( result != solution ) {
+      printf( "  Error: result( %lf ) != solution( %lf )\n", result, solution );
+    }
+  }
+
+  // Calculate time.
+  double time = timer.seconds();
+
+  // Calculate bandwidth.
+  // Each matrix A row (each of length M) is read once.
+  // The x vector (of length M) is read N times.
+  // The y vector (of length N) is read once.
+  // double Gbytes = 1.0e-9 * double( sizeof(double) * ( 2 * M * N + N ) );
+  double Gbytes = 1.0e-9 * double( sizeof(double) * ( M + M * N + N ) );
+
+  // Print results (problem size, time and bandwidth in GB/s).
+  printf( "  N( %d ) M( %d ) nrepeat ( %d ) problem( %g MB ) time( %g s ) bandwidth( %g GB/s )\n",
+          N, M, nrepeat, Gbytes * 1000, time, Gbytes * nrepeat / time );
+
+  }
+  Kokkos::finalize();
+
+  return 0;
+}
+
+void checkSizes( int &N, int &M, int &S, int &nrepeat ) {
+  // If S is undefined and N or M is undefined, set S to 2^22 or the bigger of N and M.
+  if ( S == -1 && ( N == -1 || M == -1 ) ) {
+    S = pow( 2, 22 );
+    if ( S < N ) S = N;
+    if ( S < M ) S = M;
+  }
+
+  // If S is undefined and both N and M are defined, set S = N * M.
+  if ( S == -1 ) S = N * M;
+
+  // If both N and M are undefined, fix row length to the smaller of S and 2^10 = 1024.
+  if ( N == -1 && M == -1 ) {
+    if ( S > 1024 ) {
+      M = 1024;
+    }
+    else {
+      M = S;
+    }
+  }
+
+  // If only M is undefined, set it.
+  if ( M == -1 ) M = S / N;
+
+  // If N is undefined, set it.
+  if ( N == -1 ) N = S / M;
+
+  printf( "  Total size S = %d N = %d M = %d\n", S, N, M );
+
+  // Check sizes.
+  if ( ( S < 0 ) || ( N < 0 ) || ( M < 0 ) || ( nrepeat < 0 ) ) {
+    printf( "  Sizes must be greater than 0.\n" );
+    exit( 1 );
+  }
+
+  if ( ( N * M ) != S ) {
+    printf( "  N * M != S\n" );
+    exit( 1 );
+  }
+}

Exercises/concepts/Solution/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.22)
+project(KokkosTutorialConcepts)
+include(../../common.cmake)
+
+add_executable(concepts concepts.cpp)
+target_link_libraries(concepts Kokkos::kokkos)
+