math/tensor: add mimic of Eigen::Tensor for old C++ versions

Otherwise, it relies on Eigen::Tensor with the nickname pinocchio::Tensor

src/math/tensor.hpp

+//
+// Copyright (c) 2019 INRIA
+//
+
+#ifndef __pinocchio_math_tensor_hpp__
+#define __pinocchio_math_tensor_hpp__
+
+#include "pinocchio/fwd.hpp"
+
+#ifdef PINOCCHIO_WITH_CXX11_SUPPORT
+  #include <unsupported/Eigen/CXX11/Tensor>
+#endif
+
+namespace pinocchio
+{
+
+#ifndef PINOCCHIO_WITH_CXX11_SUPPORT
+
+  // Mimic the Eigen::Tensor module only available for C++11 and more
+  template<typename Scalar_, int NumIndices_, int Options_ = 0, typename IndexType = Eigen::DenseIndex>
+  struct Tensor
+  {
+    typedef Scalar_ Scalar;
+    enum
+    {
+      Options = Options_,
+      NumIndices = NumIndices_
+    };
+    typedef IndexType Index;
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Index rank() const
+    {
+      return NumIndices;
+    }
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Index dimension(std::size_t n) const
+    {
+      assert(n <= NumIndices && "n is larger than the dimension of the tensor.");
+      return m_dimensions[n];
+    }
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Index size() const
+    {
+      return m_storage.size();
+    }
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Scalar *data()
+    {
+      return m_storage.data();
+    }
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE const Scalar *data() const 
+    {
+      return m_storage.data();
+    }
+    
+    EIGEN_DEVICE_FUNC
+    EIGEN_STRONG_INLINE Tensor& setZero()
+    {
+      return setConstant(Scalar(0));
+    }
+    
+    EIGEN_DEVICE_FUNC
+    EIGEN_STRONG_INLINE Tensor& setConstant(const Scalar & val)
+    {
+      m_storage.setConstant(val);
+      return *this;
+    }
+    
+    EIGEN_DEVICE_FUNC
+    EIGEN_STRONG_INLINE Tensor& setRandom()
+    {
+      m_storage.setRandom();
+      return *this;
+    }
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE explicit Tensor(Index dim1)
+    : m_storage(dim1)
+    {
+      m_dimensions[0] = dim1;
+      EIGEN_STATIC_ASSERT(1 == NumIndices, YOU_MADE_A_PROGRAMMING_MISTAKE)
+    }
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Tensor(Index dim1, Index dim2)
+    : m_storage(dim1*dim2)
+    {
+      m_dimensions[0] = dim1;
+      m_dimensions[1] = dim2;
+      EIGEN_STATIC_ASSERT(2 == NumIndices, YOU_MADE_A_PROGRAMMING_MISTAKE)
+    }
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Tensor(Index dim1, Index dim2, Index dim3)
+    : m_storage(dim1*dim2*dim3)
+    {
+      m_dimensions[0] = dim1;
+      m_dimensions[1] = dim2;
+      m_dimensions[2] = dim3;
+      EIGEN_STATIC_ASSERT(3 == NumIndices, YOU_MADE_A_PROGRAMMING_MISTAKE)
+    }
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Tensor(Index dim1, Index dim2, Index dim3, Index dim4)
+    : m_storage(dim1*dim2*dim3*dim4)
+    {
+      m_dimensions[0] = dim1;
+      m_dimensions[1] = dim2;
+      m_dimensions[2] = dim3;
+      m_dimensions[3] = dim4;
+      EIGEN_STATIC_ASSERT(4 == NumIndices, YOU_MADE_A_PROGRAMMING_MISTAKE)
+    }
+    
+    EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Tensor(Index dim1, Index dim2, Index dim3, Index dim4, Index dim5)
+    : m_storage(dim1*dim2*dim3*dim4*dim5)
+    {
+      m_dimensions[0] = dim1;
+      m_dimensions[1] = dim2;
+      m_dimensions[2] = dim3;
+      m_dimensions[3] = dim4;
+      m_dimensions[4] = dim5;
+      EIGEN_STATIC_ASSERT(5 == NumIndices, YOU_MADE_A_PROGRAMMING_MISTAKE)
+    }
+    
+  protected:
+    
+    typedef Eigen::Matrix<Scalar,Eigen::Dynamic,1,Options> StorageType;
+    StorageType m_storage;
+    
+    Index m_dimensions[NumIndices];
+    
+  };
+
+#else
+
+  // Use the default Eigen::Tensor module
+  template<typename Scalar_, int NumIndices_, int Options_ = 0, typename IndexType = Eigen::DenseIndex>
+  using Tensor = Eigen::Tensor<Scalar_,NumIndices_,Options_,IndexType>;
+
+#endif // ifndef PINOCCHIO_WITH_CXX11_SUPPORT
+
+}
+
+#endif // ifndef __pinocchio_math_tensor_hpp__