Add basic Kokkos support for the original tests of #783

This commit adds a test from the original Kokkos PR #783
and provides the implementation of the simplest Kokkos
features in the form of custom pushforwards. This commit
only addresses the forward mode.

unittests/Kokkos/CMakeLists.txt

@@ -1,6 +1,6 @@
 add_clad_unittest(KokkosTests
   main.cpp
-  ViewBasics.cpp
+  ViewAccess.cpp
   ParallelReduce.cpp
   ParallelFor.cpp
   )

unittests/Kokkos/KokkosImplementation.h

@@ -0,0 +1,45 @@
+// This header file contains the implementation of the Kokkos framework differentiation support in Clad in the form of custom pushforwards and pullbacks.
+
+#ifndef KOKKOS_IMPLEMENTATION
+#define KOKKOS_IMPLEMENTATION
+
+#include "clad/Differentiator/Differentiator.h"
+#include <Kokkos_Core.hpp>
+
+namespace clad {
+namespace custom_derivatives {
+    namespace class_functions {
+        /// Kokkos arrays
+        template <typename ArrayT, typename Space>
+        clad::ValueAndPushforward<Kokkos::View<ArrayT, Space>, Kokkos::View<ArrayT, Space>>
+        constructor_pushforward(clad::ConstructorPushforwardTag<Kokkos::View<ArrayT, Space>>, const ::std::string &name, const size_t& idx0, const size_t& idx1, const size_t& idx2, const size_t& idx3, const size_t& idx4, const size_t& idx5, const size_t& idx6, const size_t& idx7, const ::std::string &_d_name, const size_t& _d_idx0, const size_t& _d_idx1, const size_t& _d_idx2, const size_t& _d_idx3, const size_t& _d_idx4, const size_t& _d_idx5, const size_t& _d_idx6, const size_t& _d_idx7) {
+            return {Kokkos::View<ArrayT, Space>(name, idx0, idx1, idx2, idx3, idx4, idx5, idx6, idx7), 
+                    Kokkos::View<ArrayT, Space>("_diff_"+name, idx0, idx1, idx2, idx3, idx4, idx5, idx6, idx7)};
+        };
+
+        template <typename ArrayT, typename Layout, typename Space>
+        clad::ValueAndPushforward<Kokkos::View<ArrayT, Layout, Space>, Kokkos::View<ArrayT, Layout, Space>>
+        constructor_pushforward(clad::ConstructorPushforwardTag<Kokkos::View<ArrayT, Layout, Space>>, const ::std::string &name, const size_t& idx0, const size_t& idx1, const size_t& idx2, const size_t& idx3, const size_t& idx4, const size_t& idx5, const size_t& idx6, const size_t& idx7, const ::std::string &_d_name, const size_t& _d_idx0, const size_t& _d_idx1, const size_t& _d_idx2, const size_t& _d_idx3, const size_t& _d_idx4, const size_t& _d_idx5, const size_t& _d_idx6, const size_t& _d_idx7) {
+            return {Kokkos::View<ArrayT, Layout, Space>(name, idx0, idx1, idx2, idx3, idx4, idx5, idx6, idx7), 
+                    Kokkos::View<ArrayT, Layout, Space>("_diff_"+name, idx0, idx1, idx2, idx3, idx4, idx5, idx6, idx7)};
+        }
+    } // namespace class_functions
+
+    /// Kokkos functions
+    namespace Kokkos {
+        template <typename View1, typename View2, typename T>
+        inline void deep_copy_pushforward(const View1 &dst, const View2 &src, T param, const View1 &_d_dst, const View2 &_d_src, T _d_param) {
+            deep_copy(dst, src);
+            deep_copy(_d_dst, _d_src);
+        }
+
+
+        template<class ExecPolicy, class FunctorType>
+        inline void parallel_for_pushforward(const ::std::string &str, const ExecPolicy &policy, const FunctorType &functor, const ::std::string &_d_str, const ExecPolicy &_d_policy, const FunctorType &_d_functor) {
+            // TODO: implement parallel_for_pushforward
+            return;
+        }
+    }
+}}
+
+#endif // #ifndef KOKKOS_IMPLEMENTATION

unittests/Kokkos/ViewAccess.cpp

@@ -0,0 +1,75 @@
+// Source: https://github.com/vgvassilev/clad/pull/783/files#diff-c919937640674e1911d1f17d3df2b65426d152400589873ff9ba2f0391048d78
+// Source: https://github.com/kliegeois/clad/tree/kokkos-PR
+// Originally created by Kim Liegeois
+
+#include <Kokkos_Core.hpp>
+#include "clad/Differentiator/Differentiator.h"
+#include "gtest/gtest.h"
+#include "TestUtils.h"
+#include "KokkosImplementation.h"
+
+double f(double x, double y) {
+
+  const int N1 = 4;
+
+  Kokkos::View<double *[4], Kokkos::LayoutLeft, Kokkos::HostSpace> a("a", N1);
+  Kokkos::View<double *[4], Kokkos::LayoutLeft, Kokkos::HostSpace> b("b", N1);
+
+  a(0,0) = x;
+  b(0,0) = y;
+
+  b(0,0) += a(0,0) * b(0,0);
+
+  return a(0,0) * a(0,0) * b(0,0) + b(0,0);
+}
+
+double f_2(double x, double y) {
+
+  const int N1 = 4;
+
+  Kokkos::View<double *[4], Kokkos::LayoutLeft, Kokkos::HostSpace> a("a", N1);
+  Kokkos::View<double *[4], Kokkos::LayoutLeft, Kokkos::HostSpace> b("b", N1);
+
+  Kokkos::deep_copy(a, 3*x+y);
+  b(0,0) = x;
+  Kokkos::deep_copy(b, a);
+
+  b(0,0) += a(0,0) * b(0,0);
+
+  return a(0,0);
+}
+
+TEST(ViewAccess, Test1) {
+  EXPECT_NEAR(f(0,1), 1, 1e-8);
+  EXPECT_NEAR(f(0,2), 2, 1e-8);
+}
+
+TEST(ViewAccess, Test2) {
+
+  double tolerance = 1e-8;
+  double epsilon = 1e-6;
+
+  auto f_x = clad::differentiate(f, "x");
+
+  std::function<double(double)> f_tmp = [](double x){ return f(x,4.); };
+  double dx_f_FD = finite_difference_tangent(f_tmp, 3., epsilon);
+
+  EXPECT_NEAR(f_x.execute(3, 4),dx_f_FD,tolerance*dx_f_FD);
+
+  auto f_2_x = clad::differentiate(f_2, "x");
+
+  std::function<double(double)> f_2_tmp = [](double x){ return f_2(x,4.); };
+  double dx_f_2_FD = finite_difference_tangent(f_2_tmp, 3., epsilon);
+  EXPECT_NEAR(f_2_x.execute(3, 4),dx_f_2_FD,tolerance*dx_f_2_FD);
+
+//   TODO: uncomment this once it has been implemented
+//   auto f_grad_exe = clad::gradient(f);
+//   double dx, dy;
+//   f_grad_exe.execute(3., 4., &dx, &dy);
+//   EXPECT_NEAR(f_x.execute(3, 4),dx,tolerance*dx);
+
+//   double dx_2, dy_2;
+//   auto f_2_grad_exe = clad::gradient(f_2);
+//   f_2_grad_exe.execute(3., 4., &dx_2, &dy_2);
+//   EXPECT_NEAR(f_2_x.execute(3, 4),dx_2,tolerance*dx_2);
+}