text: // This file is part of Eigen, a lightweight C++ template library
  // for linear algebra.
  //
  // Copyright (C) 2009 Benoit Jacob <jacob.benoit.1@gmail.com>
  //
  // 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_MISC_KERNEL_H
  #define EIGEN_MISC_KERNEL_H
  
  namespace Eigen { 
  
  namespace internal {
  
  /** \class kernel_retval_base
    *
    */
  template<typename DecompositionType>
  struct traits<kernel_retval_base<DecompositionType> >
  {
    typedef typename DecompositionType::MatrixType MatrixType;
    typedef Matrix<
      typename MatrixType::Scalar,
      MatrixType::ColsAtCompileTime, // the number of rows in the "kernel matrix"
                                     // is the number of cols of the original matrix
                                     // so that the product "matrix * kernel = zero" makes sense
      Dynamic,                       // we don't know at compile-time the dimension of the kernel
      MatrixType::Options,
      MatrixType::MaxColsAtCompileTime, // see explanation for 2nd template parameter
      MatrixType::MaxColsAtCompileTime // the kernel is a subspace of the domain space,
                                       // whose dimension is the number of columns of the original matrix
    > ReturnType;
  };
  
  template<typename _DecompositionType> struct kernel_retval_base
   : public ReturnByValue<kernel_retval_base<_DecompositionType> >
  {
    typedef _DecompositionType DecompositionType;
    typedef ReturnByValue<kernel_retval_base> Base;
    typedef typename Base::Index Index;
  
    kernel_retval_base(const DecompositionType& dec)
      : m_dec(dec),
        m_rank(dec.rank()),
        m_cols(m_rank==dec.cols() ? 1 : dec.cols() - m_rank)
    {}
  
    inline Index rows() const { return m_dec.cols(); }
    inline Index cols() const { return m_cols; }
    inline Index rank() const { return m_rank; }
    inline const DecompositionType& dec() const { return m_dec; }
  
    template<typename Dest> inline void evalTo(Dest& dst) const
    {
      static_cast<const kernel_retval<DecompositionType>*>(this)->evalTo(dst);
    }
  
    protected:
      const DecompositionType& m_dec;
      Index m_rank, m_cols;
  };
  
  } // end namespace internal
  
  #define EIGEN_MAKE_KERNEL_HELPERS(DecompositionType) \
    typedef typename DecompositionType::MatrixType MatrixType; \
    typedef typename MatrixType::Scalar Scalar; \
    typedef typename MatrixType::RealScalar RealScalar; \
    typedef typename MatrixType::Index Index; \
    typedef Eigen::internal::kernel_retval_base<DecompositionType> Base; \
    using Base::dec; \
    using Base::rank; \
    using Base::rows; \
    using Base::cols; \
    kernel_retval(const DecompositionType& dec) : Base(dec) {}
  
  } // end namespace Eigen
  
  #endif // EIGEN_MISC_KERNEL_H
  