exact_error_estimator.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2025 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner

// 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 LIBMESH_EXACT_ERROR_ESTIMATOR_H
#define LIBMESH_EXACT_ERROR_ESTIMATOR_H

// Local Includes
#include "libmesh/error_estimator.h"
#include "libmesh/function_base.h"
#include "libmesh/vector_value.h"
#include "libmesh/tensor_value.h"

// C++ includes
#include <cstddef>
#include <string>
#include <vector>

namespace libMesh
{

// Forward Declarations
class Elem;
template <typename T> class FEGenericBase;
typedef FEGenericBase<Real> FEBase;
class MeshFunction;
class Point;
class Parameters;
template <typename T> class DenseVector;

class ExactErrorEstimator : public ErrorEstimator
{
public:

  ExactErrorEstimator();

  ExactErrorEstimator (const ExactErrorEstimator &) = delete;
  ExactErrorEstimator & operator= (const ExactErrorEstimator &) = delete;

  ExactErrorEstimator (ExactErrorEstimator &&) = default;
  ExactErrorEstimator & operator= (ExactErrorEstimator &&) = default;
  virtual ~ExactErrorEstimator() = default;

  void attach_exact_values (std::vector<FunctionBase<Number> *> f);

  void attach_exact_value (unsigned int sys_num,
                           FunctionBase<Number> * f);

  typedef Number (*ValueFunctionPointer)(const Point & p,
                                         const Parameters & Parameters,
                                         const std::string & sys_name,
                                         const std::string & unknown_name);
  void attach_exact_value (ValueFunctionPointer fptr);

  void attach_exact_derivs (std::vector<FunctionBase<Gradient> *> g);

  void attach_exact_deriv (unsigned int sys_num,
                           FunctionBase<Gradient> * g);

  typedef Gradient (*GradientFunctionPointer)(const Point & p,
                                              const Parameters & parameters,
                                              const std::string & sys_name,
                                              const std::string & unknown_name);
  void attach_exact_deriv (GradientFunctionPointer gptr);

  void attach_exact_hessians (std::vector<FunctionBase<Tensor> *> h);

  void attach_exact_hessian (unsigned int sys_num,
                             FunctionBase<Tensor> * h);

  typedef Tensor (*HessianFunctionPointer)(const Point & p,
                                           const Parameters & parameters,
                                           const std::string & sys_name,
                                           const std::string & unknown_name);
  void attach_exact_hessian (HessianFunctionPointer hptr);

  void attach_reference_solution (EquationSystems * es_fine);

  void extra_quadrature_order (const int extraorder)
  { _extra_order = extraorder; }

  // Bring the base class functionality into the name lookup
  // procedure.  This allows for alternative calling formats
  // defined in the base class.  Thanks Wolfgang.
  // GCC 2.95.3 cannot compile such code.  Since it was not really
  // essential to the functioning of this class, it's been removed.
  // using ErrorEstimator::estimate_error;

  virtual void estimate_error (const System & system,
                               ErrorVector & error_per_cell,
                               const NumericVector<Number> * solution_vector = nullptr,
                               bool estimate_parent_error = false) override;

  virtual ErrorEstimatorType type() const override;

private:

  ValueFunctionPointer _exact_value;

  GradientFunctionPointer _exact_deriv;

  HessianFunctionPointer _exact_hessian;

  std::vector<std::unique_ptr<FunctionBase<Number>>> _exact_values;

  std::vector<std::unique_ptr<FunctionBase<Gradient>>> _exact_derivs;

  std::vector<std::unique_ptr<FunctionBase<Tensor>>> _exact_hessians;

  EquationSystems * _equation_systems_fine;

  Real find_squared_element_error (const System & system,
                                   const std::string & var_name,
                                   const Elem * elem,
                                   const DenseVector<Number> & Uelem,
                                   FEBase * fe,
                                   MeshFunction * fine_values) const;

  void clear_functors ();

  int _extra_order;
};


} // namespace libMesh

#endif // LIBMESH_EXACT_ERROR_ESTIMATOR_H