solution_function.h

// 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 SOLUTION_FUNCTION_H
#define SOLUTION_FUNCTION_H

// libMesh includes
#include "libmesh/function_base.h"

// Example includes
#include "curl_curl_exact_solution.h"

// C++ includes
#include <memory>

using namespace libMesh;

class SolutionFunction : public FunctionBase<Number>
{
public:

  SolutionFunction(const unsigned int u_var)
    : _u_var(u_var) {}

  ~SolutionFunction() = default;

  virtual Number operator() (const Point &,
                             const Real = 0)
  { libmesh_not_implemented(); }

  virtual void operator() (const Point & p,
                           const Real,
                           DenseVector<Number> & output)
  {
    output.zero();
    // libMesh assumes each component of the vector-valued variable is stored
    // contiguously.
    output(_u_var)   = soln(p)(0);
    output(_u_var+1) = soln(p)(1);
    output(_u_var+2) = soln(p)(2);
  }

  virtual Number component(unsigned int component_in,
                           const Point & p,
                           const Real)
  {
    return soln(p)(component_in);
  }

  virtual std::unique_ptr<FunctionBase<Number>> clone() const
  { return std::make_unique<SolutionFunction>(_u_var); }

private:

  const unsigned int _u_var;
  CurlCurlExactSolution soln;
};

class SolutionGradient : public FunctionBase<Gradient>
{
public:

  SolutionGradient(const unsigned int u_var)
    : _u_var(u_var) {}

  ~SolutionGradient() = default;

  virtual Gradient operator() (const Point &, const Real = 0)
  { libmesh_not_implemented(); }

  virtual void operator() (const Point & p,
                           const Real,
                           DenseVector<Gradient> & output)
  {
    output.zero();
    output(_u_var)   = soln.grad(p).row(0);
    output(_u_var+1) = soln.grad(p).row(1);
    output(_u_var+2) = soln.grad(p).row(2);
  }

  virtual Gradient component(unsigned int component_in, const Point & p,
                             const Real)
  {
    return soln.grad(p).row(component_in);
  }

  virtual std::unique_ptr<FunctionBase<Gradient>> clone() const
  { return std::make_unique<SolutionGradient>(_u_var); }

private:

  const unsigned int _u_var;
  CurlCurlExactSolution soln;
};

#endif // SOLUTION_FUNCTION_H