const_fem_function.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2023 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_CONST_FEM_FUNCTION_H
#define LIBMESH_CONST_FEM_FUNCTION_H

// libMesh includes
#include "libmesh/dense_vector.h"
#include "libmesh/fem_function_base.h"
#include "libmesh/int_range.h"

// C++ includes
#include <memory>
#include <string>

namespace libMesh
{

// Forward declarations
class Point;

template <typename Output=Number>
class ConstFEMFunction : public FEMFunctionBase<Output>
{
public:
  ConstFEMFunction (const Output c) : _c(c) {}

  ConstFEMFunction (ConstFEMFunction &&) = default;
  ConstFEMFunction (const ConstFEMFunction &) = default;
  ConstFEMFunction & operator= (const ConstFEMFunction &) = default;
  ConstFEMFunction & operator= (ConstFEMFunction &&) = default;
  
  virtual ~ConstFEMFunction () = default;

  virtual std::unique_ptr<FEMFunctionBase<Output>> clone () const override
  {return std::make_unique<ConstFEMFunction>(*this); }

  virtual Output operator() (const FEMContext & c,
                             const Point & p,
                             const Real /* time */ = 0.) override
  { return _c; }

  virtual void operator() (const FEMContext & c,
                           const Point & p,
                           const Real,
                           DenseVector<Output> & output) override
  {
    // 将输出矢量的每个分量设置为常量值
    for (auto i : index_range(output))
      output(i) = _c;
  }

private:
  Output _c; // 存储常量值
};

} // namespace libMesh;


#endif // LIBMESH_CONST_FEM_FUNCTION_H