Symmetry.h

// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2013 Christian Seiler <christian@iwakd.de>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

#ifndef EIGEN_CXX11_TENSORSYMMETRY_SYMMETRY_H
#define EIGEN_CXX11_TENSORSYMMETRY_SYMMETRY_H

namespace Eigen {

enum {
  NegationFlag           = 0x01,
  ConjugationFlag        = 0x02
};

enum {
  GlobalRealFlag         = 0x01,
  GlobalImagFlag         = 0x02,
  GlobalZeroFlag         = 0x03
};

namespace internal {

template<std::size_t NumIndices, typename... Sym>                   struct tensor_symmetry_pre_analysis;
template<std::size_t NumIndices, typename... Sym>                   struct tensor_static_symgroup;
template<bool instantiate, std::size_t NumIndices, typename... Sym> struct tensor_static_symgroup_if;
template<typename Tensor_> struct tensor_symmetry_calculate_flags;
template<typename Tensor_> struct tensor_symmetry_assign_value;
template<typename... Sym> struct tensor_symmetry_num_indices;

} // end namespace internal

template<int One_, int Two_>
struct Symmetry
{
  static_assert(One_ != Two_, "Symmetries must cover distinct indices.");
  constexpr static int One = One_;
  constexpr static int Two = Two_;
  constexpr static int Flags = 0;
};

template<int One_, int Two_>
struct AntiSymmetry
{
  static_assert(One_ != Two_, "Symmetries must cover distinct indices.");
  constexpr static int One = One_;
  constexpr static int Two = Two_;
  constexpr static int Flags = NegationFlag;
};

template<int One_, int Two_>
struct Hermiticity
{
  static_assert(One_ != Two_, "Symmetries must cover distinct indices.");
  constexpr static int One = One_;
  constexpr static int Two = Two_;
  constexpr static int Flags = ConjugationFlag;
};

template<int One_, int Two_>
struct AntiHermiticity
{
  static_assert(One_ != Two_, "Symmetries must cover distinct indices.");
  constexpr static int One = One_;
  constexpr static int Two = Two_;
  constexpr static int Flags = ConjugationFlag | NegationFlag;
};

class DynamicSGroup;

template<typename... Gen>
class DynamicSGroupFromTemplateArgs;

template<typename... Gen>
class StaticSGroup;

template<typename... Gen>
class SGroup : public internal::tensor_symmetry_pre_analysis<internal::tensor_symmetry_num_indices<Gen...>::value, Gen...>::root_type
{
  public:
    constexpr static std::size_t NumIndices = internal::tensor_symmetry_num_indices<Gen...>::value;
    typedef typename internal::tensor_symmetry_pre_analysis<NumIndices, Gen...>::root_type Base;

    // make standard constructors + assignment operators public
    inline SGroup() : Base() { }
    inline SGroup(const SGroup<Gen...>& other) : Base(other) { }
    inline SGroup(SGroup<Gen...>&& other) : Base(other) { }
    inline SGroup<Gen...>& operator=(const SGroup<Gen...>& other) { Base::operator=(other); return *this; }
    inline SGroup<Gen...>& operator=(SGroup<Gen...>&& other) { Base::operator=(other); return *this; }

    // all else is defined in the base class
};

namespace internal {

template<typename... Sym> struct tensor_symmetry_num_indices
{
  constexpr static std::size_t value = 1;
};

template<int One_, int Two_, typename... Sym> struct tensor_symmetry_num_indices<Symmetry<One_, Two_>, Sym...>
{
private:
  constexpr static std::size_t One = static_cast<std::size_t>(One_);
  constexpr static std::size_t Two = static_cast<std::size_t>(Two_);
  constexpr static std::size_t Three = tensor_symmetry_num_indices<Sym...>::value;

  // don't use std::max, since it's not constexpr until C++14...
  constexpr static std::size_t maxOneTwoPlusOne = ((One > Two) ? One : Two) + 1;
public:
  constexpr static std::size_t value = (maxOneTwoPlusOne > Three) ? maxOneTwoPlusOne : Three;
};

template<int One_, int Two_, typename... Sym> struct tensor_symmetry_num_indices<AntiSymmetry<One_, Two_>, Sym...>
  : public tensor_symmetry_num_indices<Symmetry<One_, Two_>, Sym...> {};
template<int One_, int Two_, typename... Sym> struct tensor_symmetry_num_indices<Hermiticity<One_, Two_>, Sym...>
  : public tensor_symmetry_num_indices<Symmetry<One_, Two_>, Sym...> {};
template<int One_, int Two_, typename... Sym> struct tensor_symmetry_num_indices<AntiHermiticity<One_, Two_>, Sym...>
  : public tensor_symmetry_num_indices<Symmetry<One_, Two_>, Sym...> {};

template<std::size_t NumIndices>
struct tensor_symmetry_pre_analysis<NumIndices>
{
  typedef StaticSGroup<> root_type;
};

template<std::size_t NumIndices, typename Gen_, typename... Gens_>
struct tensor_symmetry_pre_analysis<NumIndices, Gen_, Gens_...>
{
  constexpr static std::size_t max_static_generators = 4;
  constexpr static std::size_t max_static_elements = 16;
  typedef tensor_static_symgroup_if<(sizeof...(Gens_) + 1 <= max_static_generators), NumIndices, Gen_, Gens_...> helper;
  constexpr static std::size_t possible_size = helper::size;

  typedef typename conditional<
    possible_size == 0 || possible_size >= max_static_elements,
    DynamicSGroupFromTemplateArgs<Gen_, Gens_...>,
    typename helper::type
  >::type root_type;
};

template<bool instantiate, std::size_t NumIndices, typename... Gens>
struct tensor_static_symgroup_if
{
  constexpr static std::size_t size = 0;
  typedef void type;
};

template<std::size_t NumIndices, typename... Gens>
struct tensor_static_symgroup_if<true, NumIndices, Gens...> : tensor_static_symgroup<NumIndices, Gens...> {};

template<typename Tensor_>
struct tensor_symmetry_assign_value
{
  typedef typename Tensor_::Index Index;
  typedef typename Tensor_::Scalar Scalar;
  constexpr static std::size_t NumIndices = Tensor_::NumIndices;

  static inline int run(const std::array<Index, NumIndices>& transformed_indices, int transformation_flags, int dummy, Tensor_& tensor, const Scalar& value_)
  {
    Scalar value(value_);
    if (transformation_flags & ConjugationFlag)
      value = numext::conj(value);
    if (transformation_flags & NegationFlag)
      value = -value;
    tensor.coeffRef(transformed_indices) = value;
    return dummy;
  }
};

template<typename Tensor_>
struct tensor_symmetry_calculate_flags
{
  typedef typename Tensor_::Index Index;
  constexpr static std::size_t NumIndices = Tensor_::NumIndices;

  static inline int run(const std::array<Index, NumIndices>& transformed_indices, int transform_flags, int current_flags, const std::array<Index, NumIndices>& orig_indices)
  {
    if (transformed_indices == orig_indices) {
      if (transform_flags & (ConjugationFlag | NegationFlag))
        return current_flags | GlobalImagFlag; // anti-hermitian diagonal
      else if (transform_flags & ConjugationFlag)
        return current_flags | GlobalRealFlag; // hermitian diagonal
      else if (transform_flags & NegationFlag)
        return current_flags | GlobalZeroFlag; // anti-symmetric diagonal
    }
    return current_flags;
  }
};

template<typename Tensor_, typename Symmetry_, int Flags = 0>
class tensor_symmetry_value_setter
{
  public:
    typedef typename Tensor_::Index Index;
    typedef typename Tensor_::Scalar Scalar;
    constexpr static std::size_t NumIndices = Tensor_::NumIndices;

    inline tensor_symmetry_value_setter(Tensor_& tensor, Symmetry_ const& symmetry, std::array<Index, NumIndices> const& indices)
      : m_tensor(tensor), m_symmetry(symmetry), m_indices(indices) { }

    inline tensor_symmetry_value_setter<Tensor_, Symmetry_, Flags>& operator=(Scalar const& value)
    {
      doAssign(value);
      return *this;
    }
  private:
    Tensor_& m_tensor;
    Symmetry_ m_symmetry;
    std::array<Index, NumIndices> m_indices;

    inline void doAssign(Scalar const& value)
    {
      #ifdef EIGEN_TENSOR_SYMMETRY_CHECK_VALUES
        int value_flags = m_symmetry.template apply<internal::tensor_symmetry_calculate_flags<Tensor_>, int>(m_indices, m_symmetry.globalFlags(), m_indices);
        if (value_flags & GlobalRealFlag)
          eigen_assert(numext::imag(value) == 0);
        if (value_flags & GlobalImagFlag)
          eigen_assert(numext::real(value) == 0);
      #endif
      m_symmetry.template apply<internal::tensor_symmetry_assign_value<Tensor_>, int>(m_indices, 0, m_tensor, value);
    }
};

} // end namespace internal

} // end namespace Eigen

#endif // EIGEN_CXX11_TENSORSYMMETRY_SYMMETRY_H

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