mesh_function.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2026 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_MESH_FUNCTION_H
#define LIBMESH_MESH_FUNCTION_H

// Local Includes
#include "libmesh/function_base.h"
#include "libmesh/dense_vector.h"
#include "libmesh/vector_value.h"
#include "libmesh/tensor_value.h"
#include "libmesh/tree_base.h"
#include "libmesh/parallel_object.h"

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

namespace libMesh
{


// Forward Declarations
template <typename T> class DenseVector;
class EquationSystems;
template <typename T> class NumericVector;
class DofMap;
class PointLocatorBase;

class MeshFunction : public FunctionBase<Number>,
                     public ParallelObject
{
public:

  MeshFunction (const EquationSystems & eqn_systems,
                const NumericVector<Number> & vec,
                const DofMap & dof_map,
                std::vector<unsigned int> vars,
                const FunctionBase<Number> * master=nullptr);

  MeshFunction (const EquationSystems & eqn_systems,
                const NumericVector<Number> & vec,
                const DofMap & dof_map,
                const unsigned int var,
                const FunctionBase<Number> * master=nullptr);

  MeshFunction (const MeshFunction & mf);

  MeshFunction (MeshFunction &&) = default;
  MeshFunction & operator= (const MeshFunction &) = delete;
  MeshFunction & operator= (MeshFunction &&) = delete;

  ~MeshFunction ();

  virtual void init () override;

  virtual void clear () override;

  virtual std::unique_ptr<FunctionBase<Number>> clone () const override;

  virtual Number operator() (const Point & p,
                             const Real time=0.) override;

  std::map<const Elem *, Number> discontinuous_value (const Point & p,
                                                      const Real time=0.);

  Gradient gradient (const Point & p,
                     const Real time=0.);

  std::map<const Elem *, Gradient> discontinuous_gradient (const Point & p,
                                                           const Real time=0.);

#ifdef LIBMESH_ENABLE_SECOND_DERIVATIVES

  Tensor hessian (const Point & p,
                  const Real time=0.);
#endif

  virtual void operator() (const Point & p,
                           const Real time,
                           DenseVector<Number> & output) override;

  void operator() (const Point & p,
                   const Real time,
                   DenseVector<Number> & output,
                   const std::set<subdomain_id_type> * subdomain_ids);

  void discontinuous_value (const Point & p,
                            const Real time,
                            std::map<const Elem *, DenseVector<Number>> & output);

  void discontinuous_value (const Point & p,
                            const Real time,
                            std::map<const Elem *, DenseVector<Number>> & output,
                            const std::set<subdomain_id_type> * subdomain_ids);

  void gradient (const Point & p,
                 const Real time,
                 std::vector<Gradient> & output);

  void gradient (const Point & p,
                 const Real time,
                 std::vector<Gradient> & output,
                 const std::set<subdomain_id_type> * subdomain_ids);

  void discontinuous_gradient (const Point & p,
                               const Real time,
                               std::map<const Elem *, std::vector<Gradient>> & output);

  void discontinuous_gradient (const Point & p,
                               const Real time,
                               std::map<const Elem *, std::vector<Gradient>> & output,
                               const std::set<subdomain_id_type> * subdomain_ids);

  void hessian (const Point & p,
                const Real time,
                std::vector<Tensor> & output);

  void hessian (const Point & p,
                const Real time,
                std::vector<Tensor> & output,
                const std::set<subdomain_id_type> * subdomain_ids);

  const PointLocatorBase & get_point_locator () const;
  PointLocatorBase & get_point_locator ();

  void enable_out_of_mesh_mode(const DenseVector<Number> & value);

  void enable_out_of_mesh_mode(const Number & value);

  void disable_out_of_mesh_mode();

  void set_point_locator_tolerance(Real tol);

  void unset_point_locator_tolerance();

  void set_subdomain_ids(const std::set<subdomain_id_type> * subdomain_ids);

protected:

  const Elem * find_element(const Point & p,
                            const std::set<subdomain_id_type> * subdomain_ids = nullptr) const;

  std::set<const Elem *> find_elements(const Point & p,
                                       const std::set<subdomain_id_type> * subdomain_ids = nullptr) const;

  const Elem * check_found_elem(const Elem * element, const Point & p) const;

  void _gradient_on_elem (const Point & p,
                          const Elem * element,
                          std::vector<Gradient> & output);

  const EquationSystems & _eqn_systems;

  const NumericVector<Number> & _vector;

  const DofMap & _dof_map;

  const std::vector<unsigned int> _system_vars;

  std::unique_ptr<PointLocatorBase> _point_locator;

  std::unique_ptr<std::set<subdomain_id_type>> _subdomain_ids;

  bool _out_of_mesh_mode;

  DenseVector<Number> _out_of_mesh_value;
};


} // namespace libMesh


#endif // LIBMESH_MESH_FUNCTION_H