// $Id: newton_solver.h 2788 2008-04-13 02:05:22Z roystgnr $// The libMesh Finite Element Library.// Copyright (C) 2002-2007  Benjamin S. Kirk, John W. Peterson  // This library is free software; you can redistribute it and/or// modify it under the terms of the GNU Lesser General Public// License as published by the Free Software Foundation; either// version 2.1 of the License, or (at your option) any later version.  // This library is distributed in the hope that it will be useful,// but WITHOUT ANY WARRANTY; without even the implied warranty of// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU// Lesser General Public License for more details.  // You should have received a copy of the GNU Lesser General Public// License along with this library; if not, write to the Free Software// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA#ifndef __newton_solver_h__#define __newton_solver_h__// C++ includes// Local includes#include "libmesh_common.h"#include "linear_solver.h"#include "reference_counted_object.h"#include "diff_solver.h"/** * This class defines a solver which uses the default * libMesh linear solver in a quasiNewton method to handle a  * DifferentiableSystem * * This class is part of the new DifferentiableSystem framework, * which is still experimental.  Users of this framework should * beware of bugs and future API changes. * * @author Roy H. Stogner 2006 */// ------------------------------------------------------------// Solver class definitionclass NewtonSolver : public DiffSolver{public:  /**   * Constructor. Requires a reference to the system   * to be solved.   */  NewtonSolver (sys_type& system);    /**   * Destructor.   */  virtual ~NewtonSolver ();  typedef DiffSolver Parent;  /**   * The reinitialization function.  This method is used after   * changes in the mesh.   */  virtual void reinit ();  /**   * This method performs a solve.  What occurs in   * this method will depend on the type of solver.  See   * the subclasses for more details.   */  virtual unsigned int solve ();  /**   * If this is set to true, the solver is forced to test the residual   * after each Newton step, and to reduce the length of its steps   * whenever necessary to avoid a residual increase.   * It is currently set to true by default; set it to false to   * avoid unnecessary residual assembly on well-behaved systems.   */  bool require_residual_reduction;  /**   * If require_residual_reduction is true, the solver may reduce step   * lengths when required.  If so, brent_line_search is an option.   * If brent_line_search is set to false, the solver reduces the   * length of its steps by 1/2 iteratively until it finds residual   * reduction.  If true, step lengths are first reduced by 1/2 or   * more to find some residual reduction, then Brent's method is used   * to find as much residual reduction as possible.   *   * brent_line_search is currently set to true by default.   */  bool brent_line_search;  /**   * If the quasi-Newton step length must be reduced to below this   * factor to give a residual reduction, then the Newton solver   * dies with a libmesh_error()   * It is currently set to 1e-5 by default.   */  Real minsteplength;  /**   * The tolerance for linear solves is kept below this multiplier (which   * defaults to 1e-3) times the norm of the current nonlinear residual   */  Real linear_tolerance_multiplier;protected:  /**   * The \p LinearSolver defines the interface used to   * solve the linear_implicit system.  This class handles all the   * details of interfacing with various linear algebra packages   * like PETSc or LASPACK.   */  AutoPtr<LinearSolver<Number> > linear_solver;  /**   * This does a line search in the direction opposite linear_solution   * to try and minimize the residual of newton_iterate.   * newton_iterate is moved to the end of the quasiNewton step, and   * the return value is the substep size.   */  Real line_search(Real tol, Real last_residual, Real current_residual,		   NumericVector<Number> &newton_iterate,		   const NumericVector<Number> &linear_solution);  /**   * This prints output for the convergence criteria based on   * by the given residual and step size.   */  void print_convergence(unsigned int step_num,			 Real current_residual,			 Real step_norm,			 bool linear_solve_finished);  /**   * This returns true if a convergence criterion has been passed   * by the given residual and step size; false otherwise.   */  bool test_convergence(Real current_residual,			Real step_norm,			bool linear_solve_finished);};#endif // #define __newton_solver_h__