From c53f783705e05c07d9f1c02ab12fdb5d57f1a7a9 Mon Sep 17 00:00:00 2001
From: Benoit Steiner <benoit.steiner.goog@gmail.com>
Date: Thu, 1 Sep 2016 11:41:27 -0700
Subject: [PATCH] Updated the contraction code to support constant inputs.

---
 .../CXX11/src/Tensor/TensorContraction.h      |  3 ++-
 unsupported/test/cxx11_tensor_contraction.cpp | 23 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorContraction.h b/unsupported/Eigen/CXX11/src/Tensor/TensorContraction.h
index a6001074b..20b29e5fd 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorContraction.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorContraction.h
@@ -25,7 +25,8 @@ template<typename Dimensions, typename LhsXprType, typename RhsXprType>
 struct traits<TensorContractionOp<Dimensions, LhsXprType, RhsXprType> >
 {
   // Type promotion to handle the case where the types of the lhs and the rhs are different.
-  typedef typename gebp_traits<typename LhsXprType::Scalar, typename RhsXprType::Scalar>::ResScalar Scalar;
+  typedef typename gebp_traits<typename remove_const<typename LhsXprType::Scalar>::type,
+                               typename remove_const<typename RhsXprType::Scalar>::type>::ResScalar Scalar;
 
   typedef typename promote_storage_type<typename traits<LhsXprType>::StorageKind,
                                         typename traits<RhsXprType>::StorageKind>::ret StorageKind;
diff --git a/unsupported/test/cxx11_tensor_contraction.cpp b/unsupported/test/cxx11_tensor_contraction.cpp
index 73623b2ed..ace97057f 100644
--- a/unsupported/test/cxx11_tensor_contraction.cpp
+++ b/unsupported/test/cxx11_tensor_contraction.cpp
@@ -489,6 +489,27 @@ static void test_tensor_product()
 }
 
 
+template<int DataLayout>
+static void test_const_inputs()
+{
+  Tensor<float, 2, DataLayout> in1(2, 3);
+  Tensor<float, 2, DataLayout> in2(3, 2);
+  in1.setRandom();
+  in2.setRandom();
+
+  TensorMap<Tensor<const float, 2, DataLayout> > mat1(in1.data(), 2, 3);
+  TensorMap<Tensor<const float, 2, DataLayout> > mat2(in2.data(), 3, 2);
+  Tensor<float, 2, DataLayout> mat3(2,2);
+
+  Eigen::array<DimPair, 1> dims = {{DimPair(1, 0)}};
+  mat3 = mat1.contract(mat2, dims);
+
+  VERIFY_IS_APPROX(mat3(0,0), mat1(0,0)*mat2(0,0) + mat1(0,1)*mat2(1,0) + mat1(0,2)*mat2(2,0));
+  VERIFY_IS_APPROX(mat3(0,1), mat1(0,0)*mat2(0,1) + mat1(0,1)*mat2(1,1) + mat1(0,2)*mat2(2,1));
+  VERIFY_IS_APPROX(mat3(1,0), mat1(1,0)*mat2(0,0) + mat1(1,1)*mat2(1,0) + mat1(1,2)*mat2(2,0));
+  VERIFY_IS_APPROX(mat3(1,1), mat1(1,0)*mat2(0,1) + mat1(1,1)*mat2(1,1) + mat1(1,2)*mat2(2,1));
+}
+
 void test_cxx11_tensor_contraction()
 {
   CALL_SUBTEST(test_evals<ColMajor>());
@@ -519,4 +540,6 @@ void test_cxx11_tensor_contraction()
   CALL_SUBTEST(test_small_blocking_factors<RowMajor>());
   CALL_SUBTEST(test_tensor_product<ColMajor>());
   CALL_SUBTEST(test_tensor_product<RowMajor>());
+  CALL_SUBTEST(test_const_inputs<ColMajor>());
+  CALL_SUBTEST(test_const_inputs<RowMajor>());
 }