SparseDiagonalProduct.h

// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2009-2015 Gael Guennebaud <gael.guennebaud@inria.fr>
//
// 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_SPARSE_DIAGONAL_PRODUCT_H
#define EIGEN_SPARSE_DIAGONAL_PRODUCT_H

// IWYU pragma: private
#include "./InternalHeaderCheck.h"

namespace Eigen {

// The product of a diagonal matrix with a sparse matrix can be easily
// implemented using expression template.
// We have two consider very different cases:
// 1 - diag * row-major sparse
//     => each inner vector <=> scalar * sparse vector product
//     => so we can reuse CwiseUnaryOp::InnerIterator
// 2 - diag * col-major sparse
//     => each inner vector <=> densevector * sparse vector cwise product
//     => again, we can reuse specialization of CwiseBinaryOp::InnerIterator
//        for that particular case
// The two other cases are symmetric.

namespace internal {

enum { SDP_AsScalarProduct, SDP_AsCwiseProduct };

template <typename SparseXprType, typename DiagonalCoeffType, int SDP_Tag>
struct sparse_diagonal_product_evaluator;

template <typename Lhs, typename Rhs, int ProductTag>
struct product_evaluator<Product<Lhs, Rhs, DefaultProduct>, ProductTag, DiagonalShape, SparseShape>
    : public sparse_diagonal_product_evaluator<Rhs, typename Lhs::DiagonalVectorType,
                                               Rhs::Flags & RowMajorBit ? SDP_AsScalarProduct : SDP_AsCwiseProduct> {
  typedef Product<Lhs, Rhs, DefaultProduct> XprType;
  enum { CoeffReadCost = HugeCost, Flags = Rhs::Flags & RowMajorBit, Alignment = 0 };  // FIXME CoeffReadCost & Flags

  typedef sparse_diagonal_product_evaluator<Rhs, typename Lhs::DiagonalVectorType,
                                            Rhs::Flags & RowMajorBit ? SDP_AsScalarProduct : SDP_AsCwiseProduct>
      Base;
  explicit product_evaluator(const XprType &xpr) : Base(xpr.rhs(), xpr.lhs().diagonal()) {}
};

template <typename Lhs, typename Rhs, int ProductTag>
struct product_evaluator<Product<Lhs, Rhs, DefaultProduct>, ProductTag, SparseShape, DiagonalShape>
    : public sparse_diagonal_product_evaluator<Lhs, Transpose<const typename Rhs::DiagonalVectorType>,
                                               Lhs::Flags & RowMajorBit ? SDP_AsCwiseProduct : SDP_AsScalarProduct> {
  typedef Product<Lhs, Rhs, DefaultProduct> XprType;
  enum { CoeffReadCost = HugeCost, Flags = Lhs::Flags & RowMajorBit, Alignment = 0 };  // FIXME CoeffReadCost & Flags

  typedef sparse_diagonal_product_evaluator<Lhs, Transpose<const typename Rhs::DiagonalVectorType>,
                                            Lhs::Flags & RowMajorBit ? SDP_AsCwiseProduct : SDP_AsScalarProduct>
      Base;
  explicit product_evaluator(const XprType &xpr) : Base(xpr.lhs(), xpr.rhs().diagonal().transpose()) {}
};

template <typename SparseXprType, typename DiagonalCoeffType>
struct sparse_diagonal_product_evaluator<SparseXprType, DiagonalCoeffType, SDP_AsScalarProduct> {
 protected:
  typedef typename evaluator<SparseXprType>::InnerIterator SparseXprInnerIterator;
  typedef typename SparseXprType::Scalar Scalar;

 public:
  class InnerIterator : public SparseXprInnerIterator {
   public:
    InnerIterator(const sparse_diagonal_product_evaluator &xprEval, Index outer)
        : SparseXprInnerIterator(xprEval.m_sparseXprImpl, outer), m_coeff(xprEval.m_diagCoeffImpl.coeff(outer)) {}

    EIGEN_STRONG_INLINE Scalar value() const { return m_coeff * SparseXprInnerIterator::value(); }

   protected:
    typename DiagonalCoeffType::Scalar m_coeff;
  };

  sparse_diagonal_product_evaluator(const SparseXprType &sparseXpr, const DiagonalCoeffType &diagCoeff)
      : m_sparseXprImpl(sparseXpr), m_diagCoeffImpl(diagCoeff) {}

  Index nonZerosEstimate() const { return m_sparseXprImpl.nonZerosEstimate(); }

 protected:
  evaluator<SparseXprType> m_sparseXprImpl;
  evaluator<DiagonalCoeffType> m_diagCoeffImpl;
};

template <typename SparseXprType, typename DiagCoeffType>
struct sparse_diagonal_product_evaluator<SparseXprType, DiagCoeffType, SDP_AsCwiseProduct> {
  typedef typename SparseXprType::Scalar Scalar;
  typedef typename SparseXprType::StorageIndex StorageIndex;

  typedef typename nested_eval<DiagCoeffType, SparseXprType::IsRowMajor ? SparseXprType::RowsAtCompileTime
                                                                        : SparseXprType::ColsAtCompileTime>::type
      DiagCoeffNested;

  class InnerIterator {
    typedef typename evaluator<SparseXprType>::InnerIterator SparseXprIter;

   public:
    InnerIterator(const sparse_diagonal_product_evaluator &xprEval, Index outer)
        : m_sparseIter(xprEval.m_sparseXprEval, outer), m_diagCoeffNested(xprEval.m_diagCoeffNested) {}

    inline Scalar value() const { return m_sparseIter.value() * m_diagCoeffNested.coeff(index()); }
    inline StorageIndex index() const { return m_sparseIter.index(); }
    inline Index outer() const { return m_sparseIter.outer(); }
    inline Index col() const { return SparseXprType::IsRowMajor ? m_sparseIter.index() : m_sparseIter.outer(); }
    inline Index row() const { return SparseXprType::IsRowMajor ? m_sparseIter.outer() : m_sparseIter.index(); }

    EIGEN_STRONG_INLINE InnerIterator &operator++() {
      ++m_sparseIter;
      return *this;
    }
    inline operator bool() const { return m_sparseIter; }

   protected:
    SparseXprIter m_sparseIter;
    DiagCoeffNested m_diagCoeffNested;
  };

  sparse_diagonal_product_evaluator(const SparseXprType &sparseXpr, const DiagCoeffType &diagCoeff)
      : m_sparseXprEval(sparseXpr), m_diagCoeffNested(diagCoeff) {}

  Index nonZerosEstimate() const { return m_sparseXprEval.nonZerosEstimate(); }

 protected:
  evaluator<SparseXprType> m_sparseXprEval;
  DiagCoeffNested m_diagCoeffNested;
};

}  // end namespace internal

}  // end namespace Eigen

#endif  // EIGEN_SPARSE_DIAGONAL_PRODUCT_H