From 1c8312c811344beaa06f7ae9258f66c38337c607 Mon Sep 17 00:00:00 2001
From: Benoit Steiner <benoit.steiner.goog@gmail.com>
Date: Mon, 26 Oct 2015 14:29:26 -0700
Subject: [PATCH] Started to add support for tensors of rank 0

---
 unsupported/Eigen/CXX11/src/Tensor/Tensor.h   | 31 +++++++++++++++++++
 unsupported/Eigen/CXX11/src/Tensor/TensorIO.h |  5 ++-
 .../CXX11/src/Tensor/TensorInitializer.h      | 12 +++++++
 .../Eigen/CXX11/src/Tensor/TensorStorage.h    | 12 +++++--
 4 files changed, 57 insertions(+), 3 deletions(-)

diff --git a/unsupported/Eigen/CXX11/src/Tensor/Tensor.h b/unsupported/Eigen/CXX11/src/Tensor/Tensor.h
index 3ac465d24..0df1345c2 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/Tensor.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/Tensor.h
@@ -140,6 +140,12 @@ class Tensor : public TensorBase<Tensor<Scalar_, NumIndices_, Options_, IndexTyp
     }
 #endif
 
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE const Scalar& coeff() const
+    {
+      EIGEN_STATIC_ASSERT(NumIndices == 0, YOU_MADE_A_PROGRAMMING_MISTAKE);
+      return m_storage.data()[0];
+    }
+
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE const Scalar& coeff(Index index) const
     {
       eigen_internal_assert(index >= 0 && index < size());
@@ -174,6 +180,12 @@ class Tensor : public TensorBase<Tensor<Scalar_, NumIndices_, Options_, IndexTyp
     }
 #endif
 
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Scalar& coeffRef()
+    {
+      EIGEN_STATIC_ASSERT(NumIndices == 0, YOU_MADE_A_PROGRAMMING_MISTAKE);
+      return m_storage.data()[0];
+    }
+
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Scalar& coeffRef(Index index)
     {
       eigen_internal_assert(index >= 0 && index < size());
@@ -234,6 +246,12 @@ class Tensor : public TensorBase<Tensor<Scalar_, NumIndices_, Options_, IndexTyp
       return coeff(index);
     }
 
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE const Scalar& operator()() const
+    {
+      EIGEN_STATIC_ASSERT(NumIndices == 0, YOU_MADE_A_PROGRAMMING_MISTAKE);
+      return coeff();
+    }
+
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE const Scalar& operator[](Index index) const
     {
       // The bracket operator is only for vectors, use the parenthesis operator instead.
@@ -295,6 +313,12 @@ class Tensor : public TensorBase<Tensor<Scalar_, NumIndices_, Options_, IndexTyp
       return coeffRef(index);
     }
 
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Scalar& operator()()
+    {
+      EIGEN_STATIC_ASSERT(NumIndices == 0, YOU_MADE_A_PROGRAMMING_MISTAKE);
+      return coeffRef();
+    }
+
     EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Scalar& operator[](Index index)
     {
       // The bracket operator is only for vectors, use the parenthesis operator instead
@@ -433,6 +457,13 @@ class Tensor : public TensorBase<Tensor<Scalar_, NumIndices_, Options_, IndexTyp
       resize(dims);
     }
 
+    EIGEN_DEVICE_FUNC
+    void resize()
+    {
+      EIGEN_STATIC_ASSERT(NumIndices == 0, YOU_MADE_A_PROGRAMMING_MISTAKE);
+      // Nothing to do: rank 0 tensors have fixed size
+    }
+
     /** Custom Dimension */
 #ifdef EIGEN_HAS_SFINAE
     template<typename CustomDimension,
diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorIO.h b/unsupported/Eigen/CXX11/src/Tensor/TensorIO.h
index 3b6f2c730..38a833f82 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorIO.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorIO.h
@@ -33,7 +33,10 @@ std::ostream& operator << (std::ostream& os, const TensorBase<T, ReadOnlyAccesso
   const Index total_size = internal::array_prod(tensor.dimensions());
 
   // Print the tensor as a 1d vector or a 2d matrix.
-  if (internal::array_size<Dimensions>::value == 1) {
+  static const int rank = internal::array_size<Dimensions>::value;
+  if (rank == 0) {
+    os << tensor.coeff(0);
+  } else if (rank == 1) {
     Map<const Array<Scalar, Dynamic, 1> > array(const_cast<Scalar*>(tensor.data()), total_size);
     os << array;
   } else {
diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorInitializer.h b/unsupported/Eigen/CXX11/src/Tensor/TensorInitializer.h
index 4303e3536..ad2a1e6ac 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorInitializer.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorInitializer.h
@@ -55,6 +55,18 @@ struct Initializer<Derived, 1> {
   }
 };
 
+template <typename Derived>
+struct Initializer<Derived, 0> {
+  typedef typename traits<Derived>::Scalar InitList;
+
+  static void run(TensorEvaluator<Derived, DefaultDevice>& tensor,
+                  Eigen::array<typename traits<Derived>::Index, traits<Derived>::NumDimensions>*/* indices*/,
+                  const InitList& v) {
+    tensor.coeffRef(0) = v;
+  }
+};
+
+
 template <typename Derived, int N>
 void initialize_tensor(TensorEvaluator<Derived, DefaultDevice>& tensor,
                        const typename Initializer<Derived, traits<Derived>::NumDimensions>::InitList& vals) {
diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorStorage.h b/unsupported/Eigen/CXX11/src/Tensor/TensorStorage.h
index 9e4cf039d..ee6f14b8f 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorStorage.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorStorage.h
@@ -71,7 +71,11 @@ class TensorStorage<T, DSizes<IndexType, NumIndices_>, Options_>
     typedef DSizes<IndexType, NumIndices_> Dimensions;
     typedef TensorStorage<T, DSizes<IndexType, NumIndices_>, Options_> Self;
 
-    EIGEN_DEVICE_FUNC TensorStorage() : m_data(0), m_dimensions() {}
+    EIGEN_DEVICE_FUNC TensorStorage() : m_data(0), m_dimensions() {
+      if (NumIndices_ == 0) {
+	m_data = internal::conditional_aligned_new_auto<T,(Options_&DontAlign)==0>(1);
+      }
+    }
     EIGEN_DEVICE_FUNC TensorStorage(internal::constructor_without_unaligned_array_assert)
       : m_data(0), m_dimensions(internal::template repeat<NumIndices_, Index>(0)) {}
     EIGEN_DEVICE_FUNC TensorStorage(Index size, const array<Index, NumIndices_>& dimensions)
@@ -101,13 +105,17 @@ class TensorStorage<T, DSizes<IndexType, NumIndices_>, Options_>
 
     EIGEN_DEVICE_FUNC void resize(Index size, const array<Index, NumIndices_>& nbDimensions)
     {
+      eigen_assert(size >= 1);
       const Index currentSz = internal::array_prod(m_dimensions);
       if(size != currentSz)
       {
         internal::conditional_aligned_delete_auto<T,(Options_&DontAlign)==0>(m_data, currentSz);
         if (size)
           m_data = internal::conditional_aligned_new_auto<T,(Options_&DontAlign)==0>(size);
-        else
+        else if (NumIndices_ == 0) {
+	  m_data = internal::conditional_aligned_new_auto<T,(Options_&DontAlign)==0>(1);
+	}
+	else 
           m_data = 0;
         EIGEN_INTERNAL_DENSE_STORAGE_CTOR_PLUGIN
       }