// Copyright (C) 2004, 2006 International Business Machines and others.
// All Rights Reserved.
// This code is published under the Eclipse Public License.
//
// $Id$
//
// Authors:  Carl Laird, Andreas Waechter     IBM    2004-08-13

#ifndef __IPPDSYSTEMSOLVER_HPP__
#define __IPPDSYSTEMSOLVER_HPP__

#include "IpUtils.hpp"
#include "IpSymMatrix.hpp"
#include "IpAlgStrategy.hpp"
#include "IpIteratesVector.hpp"

namespace Ipopt
{

  /** Pure Primal Dual System Solver Base Class.
   *  This is the base class for all derived Primal-Dual System Solver Types.
   *
   *  Here, we understand the primal-dual system as the following linear
   *  system:
   *
   *  \f$
   *  \left[\begin{array}{cccccccc}
   *  W & 0 & J_c^T & J_d^T & -P^x_L & P^x_U & 0 & 0 \\
   *  0 & 0 & 0 & -I & 0 & 0 & -P_L^d & P_U^d \\
   *  J_c & 0 & 0 & 0 & 0 & 0 & 0 & 0\\
   *  J_d & -I & 0 & 0 & 0 & 0 & 0 & 0\\
   *  Z_L(P_L^x)^T & 0 & 0 & 0 & Sl^x_L & 0 & 0 & 0\\
   *  -Z_U(P_U^x)^T & 0 & 0 & 0 & 0 & Sl^x_U & 0 & 0\\
   *  0 & V_L(P_L^d)^T & 0 & 0 & 0 & 0 & Sl^s_L & 0 \\
   *  0 & -V_U(P_U^d)^T & 0 & 0 & 0 & 0 & 0 & Sl^s_U \\
   *  \end{array}\right]
   *  \left(\begin{array}{c}
   *  sol_x\\ sol_s\\ sol_c\\ sol_d\\ sol^z_L\\ sol^z_U\\ sol^v_L\\
   *  sol^v_U
   *  \end{array}\right) = 
   *  \left(\begin{array}{c}
   *  rhs_x\\ rhs_s\\ rhs_c\\ rhs_d\\ rhs^z_L\\ rhs^z_U\\ rhs^v_L\\
   *  rhs^v_U
   *  \end{array}\right)
   *  \f$
   *
   *  Here, \f$Sl^x_L = (P^x_L)^T x - x_L\f$, 
   *  \f$Sl^x_U = x_U - (P^x_U)^T x\f$, \f$Sl^d_L = (P^d_L)^T d(x) - d_L\f$,
   *  \f$Sl^d_U = d_U - (P^d_U)^T d(x)\f$.  The results returned to the
   *  caller is \f$res = \alpha * sol + \beta * res\f$.
   *
   *  The solution of this linear system (in order to compute the search
   *  direction of the algorthim) usually requires a considerable amount of
   *  computation time.  Therefore, it is important to tailor the solution
   *  of this system to the characteristics of the problem.  The purpose of
   *  this base class is to provide a generic interface to the algorithm
   *  that it can use whenever it requires a solution of the above system.
   *  Particular implementation can then be written to provide the methods
   *  defined here.
   *
   *  It is implicitly assumed here, that the upper left 2 by 2 block
   *  is possibly modified (implicitly or explicitly) so that its
   *  projection onto the null space of the overall constraint
   *  Jacobian \f$\left[\begin{array}{cc}J_c & 0\\J_d &
   *  -I\end{array}\right]\f$ is positive definite.  This is necessary
   *  to guarantee certain descent properties of the resulting search
   *  direction.  For example, in the full space implementation, a
   *  multiple of the identity might be added to the upper left 2 by 2
   *  block.
   *
   *  Note that the Solve method might be called several times for different
   *  right hand sides, but with identical data.  Therefore, if possible,
   *  an implemetation of PDSystem should check whether the incoming data has
   *  changed, and not redo factorization etc. unless necessary.
   */
  class PDSystemSolver: public AlgorithmStrategyObject
  {
  public:
    /** @name /Destructor */
    //@{
    /** Default Constructor */
    PDSystemSolver()
    {}

    /** Default destructor */
    virtual ~PDSystemSolver()
    {}
    //@}

    /** overloaded from AlgorithmStrategyObject */
    virtual bool InitializeImpl(const OptionsList& options,
                                const std::string& prefix) = 0;

    /** Solve the primal dual system, given one right hand side.  If
     *  the flag allow_inexact is set to true, it is not necessary to
     *  solve the system to best accuracy; for example, we don't want
     *  iterative refinement during the computation of the second
     *  order correction.  On the other hand, if improve_solution is
     *  true, the solution given in res should be improved (here beta
     *  has to be zero, and res is assume to be the solution for the
     *  system using rhs, without the factor alpha...).  THe return
     *  value is false, if a solution could not be computed (for
     *  example, when the Hessian regularization parameter becomes too
     *  large.)
     */
    virtual bool Solve(Number alpha,
                       Number beta,
                       const IteratesVector& rhs,
                       IteratesVector& res,
                       bool allow_inexact=false,
                       bool improve_solution=false) =0;

  private:
    /**@name Default Compiler Generated Methods
     * (Hidden to avoid implicit creation/calling).
     * These methods are not implemented and 
     * we do not want the compiler to implement
     * them for us, so we declare them private
     * and do not define them. This ensures that
     * they will not be implicitly created/called. */
    //@{
    /** Overloaded Equals Operator */
    PDSystemSolver& operator=(const PDSystemSolver&);
    //@}
  };


} // namespace Ipopt

#endif
