// @HEADER
//
// ***********************************************************************
//
//        MueLu: A package for multigrid based preconditioning
//                  Copyright 2012 Sandia Corporation
//
// Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation,
// the U.S. Government retains certain rights in this software.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// 3. Neither the name of the Corporation nor the names of the
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY SANDIA CORPORATION "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SANDIA CORPORATION OR THE
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Questions? Contact
//                    Jonathan Hu       (jhu@sandia.gov)
//                    Andrey Prokopenko (aprokop@sandia.gov)
//                    Ray Tuminaro      (rstumin@sandia.gov)
//
// ***********************************************************************
//
// @HEADER
#ifndef MUELU_PROJECTORSMOOTHER_DECL_HPP
#define MUELU_PROJECTORSMOOTHER_DECL_HPP

#include <Xpetra_Matrix_fwd.hpp>
#include <Xpetra_MultiVector_fwd.hpp>

#include "MueLu_ConfigDefs.hpp"

#include "MueLu_SmootherPrototype.hpp"
#include "MueLu_FactoryBase_fwd.hpp"
#include "MueLu_Utilities_fwd.hpp"

namespace MueLu {

  /*!
    @class ProjectorSmoother
    @ingroup MueLuSmootherClasses 
    @brief This class enables the elimination of the nullspace component of the solution through the use of projection

    The solution of the coarsest level system may have a significant nullspace component. We can try to eliminate it through the use of nullspaces.
    Due to our construction algorithms, we always have some nullspace vectors on the coarsest level. However, we do not know if they are true
    nullspace vectors or are only approximations to them.

    We will use the Rayleigh quotiont to separate the true nullspace vectors. If Rayleigh quotient is less than specified epsilon, we consider the
    vector to be a true nullspace vector.

    After we separate true nullspace vectors, we project our solution to the space orthogonal to them. To do that in a computationally efficient manner,
    in the Setup stage we orthonormalize the selected nullspace components.
  */

  template <class Scalar = SmootherPrototype<>::scalar_type,
            class LocalOrdinal = typename SmootherPrototype<Scalar>::local_ordinal_type,
            class GlobalOrdinal = typename SmootherPrototype<Scalar, LocalOrdinal>::global_ordinal_type,
            class Node = typename SmootherPrototype<Scalar, LocalOrdinal, GlobalOrdinal>::node_type>
  class ProjectorSmoother : public SmootherPrototype<Scalar,LocalOrdinal,GlobalOrdinal,Node>
  {
#undef MUELU_PROJECTORSMOOTHER_SHORT
#include "MueLu_UseShortNames.hpp"

  public:

    //! @name Constructors / destructors
    //@{

    //! @brief Constructor
    ProjectorSmoother(RCP<SmootherPrototype> coarseSolver);

    //! Destructor
    virtual ~ProjectorSmoother();
    //@}

    //! Input
    //@{

    void DeclareInput(Level &currentLevel) const;

    //@}

    //! @name Setup and Apply methods.
    //@{

    //! @brief Set up the direct solver.
    void Setup(Level &currentLevel);

    /*! @brief Apply the direct solver.
    Solves the linear system <tt>AX=B</tt> using the constructed solver.
    @param X initial guess
    @param B right-hand side
    @param InitialGuessIsZero This option has no effect.
    */
    void Apply(MultiVector& X, const MultiVector& B, bool InitialGuessIsZero = false) const;
    //@}

    RCP<SmootherPrototype> Copy() const;

    //! @name Overridden from Teuchos::Describable
    //@{

    //! Return a simple one-line description of this object.
    std::string description() const;

    //! Print the object with some verbosity level to an FancyOStream object.
    //using MueLu::Describable::describe; // overloading, not hiding
    void print(Teuchos::FancyOStream &out, const VerbLevel verbLevel = Default) const;

    //@}

  private:
    RCP<MultiVector>             Borth_;
    RCP<SmootherPrototype>       coarseSolver_;

  }; // class ProjectorSmoother

} // namespace MueLu

#define MUELU_PROJECTORSMOOTHER_SHORT
#endif // MUELU_PROJECTORSMOOTHER_DECL_HPP
