KroneckerTensorProduct.h

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// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2011 Kolja Brix <brix@igpm.rwth-aachen.de>
// Copyright (C) 2011 Andreas Platen <andiplaten@gmx.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 KRONECKER_TENSOR_PRODUCT_H
#define KRONECKER_TENSOR_PRODUCT_H


namespace Eigen { 

namespace internal {

template<typename Derived_A, typename Derived_B, typename Derived_AB>
void kroneckerProduct_full(const Derived_A& A, const Derived_B& B, Derived_AB & AB)
{
  const unsigned int Ar = A.rows(),
                     Ac = A.cols(),
                     Br = B.rows(),
                     Bc = B.cols();
  for (unsigned int i=0; i<Ar; ++i)
    for (unsigned int j=0; j<Ac; ++j)
      AB.block(i*Br,j*Bc,Br,Bc) = A(i,j)*B;
}


template<typename Derived_A, typename Derived_B, typename Derived_AB>
void kroneckerProduct_sparse(const Derived_A &A, const Derived_B &B, Derived_AB &AB)
{
  const unsigned int Ar = A.rows(),
                     Ac = A.cols(),
                     Br = B.rows(),
                     Bc = B.cols();
  AB.resize(Ar*Br,Ac*Bc);
  AB.resizeNonZeros(0);
  AB.reserve(A.nonZeros()*B.nonZeros());

  for (int kA=0; kA<A.outerSize(); ++kA)
  {
    for (int kB=0; kB<B.outerSize(); ++kB)
    {
      for (typename Derived_A::InnerIterator itA(A,kA); itA; ++itA)
      {
        for (typename Derived_B::InnerIterator itB(B,kB); itB; ++itB)
        {
          const unsigned int iA = itA.row(),
                             jA = itA.col(),
                             iB = itB.row(),
                             jB = itB.col(),
                             i  = iA*Br + iB,
                             j  = jA*Bc + jB;
          AB.insert(i,j) = itA.value() * itB.value();
        }
      }
    }
  }
}

} // end namespace internal



template<typename A,typename B,typename CScalar,int CRows,int CCols, int COptions, int CMaxRows, int CMaxCols>
void kroneckerProduct(const MatrixBase<A>& a, const MatrixBase<B>& b, Matrix<CScalar,CRows,CCols,COptions,CMaxRows,CMaxCols>& c)
{
  c.resize(a.rows()*b.rows(),a.cols()*b.cols());
  internal::kroneckerProduct_full(a.derived(), b.derived(), c);
}

template<typename A,typename B,typename C>
void kroneckerProduct(const MatrixBase<A>& a, const MatrixBase<B>& b, MatrixBase<C> const & c_)
{
  MatrixBase<C>& c = const_cast<MatrixBase<C>& >(c_);
  internal::kroneckerProduct_full(a.derived(), b.derived(), c.derived());
}

template<typename A,typename B,typename C>
void kroneckerProduct(const MatrixBase<A>& a, const SparseMatrixBase<B>& b, SparseMatrixBase<C>& c)
{
  internal::kroneckerProduct_sparse(a.derived(), b.derived(), c.derived());
}

template<typename A,typename B,typename C>
void kroneckerProduct(const SparseMatrixBase<A>& a, const MatrixBase<B>& b, SparseMatrixBase<C>& c)
{
  internal::kroneckerProduct_sparse(a.derived(), b.derived(), c.derived());
}

template<typename A,typename B,typename C>
void kroneckerProduct(const SparseMatrixBase<A>& a, const SparseMatrixBase<B>& b, SparseMatrixBase<C>& c)
{
  internal::kroneckerProduct_sparse(a.derived(), b.derived(), c.derived());
}

} // end namespace Eigen

#endif // KRONECKER_TENSOR_PRODUCT_H