ConstantGridFunction.hpp 5.19 KB
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#pragma once

#include <functional>
#include <type_traits>

#include <dune/common/diagonalmatrix.hh>
#include <dune/common/fmatrix.hh>
#include <dune/common/fvector.hh>
#include <dune/functions/common/defaultderivativetraits.hh>

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#include <amdis/common/TypeTraits.hpp>
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#include <amdis/gridfunctions/AnalyticGridFunction.hpp>
#include <amdis/gridfunctions/GridFunctionConcepts.hpp>
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namespace AMDiS
{
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#ifndef DOXYGEN
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  template <class Signature, class LocalContext, class Function>
  class ConstantLocalFunction;
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#endif
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  /// \brief LocalFunction of a Gridfunction returning a constant value.
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  template <class R, class D, class LC, class T>
  class ConstantLocalFunction<R(D), LC, T>
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  {
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  public:
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    /// The LocalDomain this LocalFunction can be evaluated in
    using Domain = D;
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    /// The range type of the LocalFunction
    using Range = R;
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    /// This LocalFunction has its own \ref derivative() function
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    enum { hasDerivative = true };

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  private:
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    using Geometry = typename LC::Geometry;
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  public:
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    /// \brief Constructor. Stores the constant value.
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    ConstantLocalFunction(T const& value)
      : value_(value)
    {}

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    void bind(LC const& /*element*/) { /* do nothing */ }
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    void unbind() { /* do nothing */ }
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    /// Return the constant `value_`.
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    Range const& operator()(Domain const& /*local*/) const
    {
      return value_;
    }

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    /// \brief Create a \ref ConstantLocalFunction representing the derivative
    /// of a constant function, that ist, the value 0.
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    auto derivative() const
    {
      using RawSignature = typename Dune::Functions::SignatureTraits<R(D)>::RawSignature;
      using DerivativeRange = typename Dune::Functions::DefaultDerivativeTraits<RawSignature>::Range;
      DerivativeRange diff(0);
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      return ConstantLocalFunction<DerivativeRange(D),LC,DerivativeRange>{diff};
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    }

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    /// Return the constant polynomial order 0.
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    int order() const
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    {
      return 0;
    }

  private:
    T value_;
  };

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  /// \relates ConstantLocalFunction
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  template <class R, class D, class LC, class T>
  auto derivative(ConstantLocalFunction<R(D), LC, T> const& lf)
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  {
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    return lf.derivative();
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  }

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  /// \brief Gridfunction returning a constant value.
  /**
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   * \ingroup GridFunctions
   *
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   * A stored constant is return in global and local evaluation of this functor.
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   * Maybe used with arithmetic types and vectors/matrices of arithmetic types.
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   * It is also allowed to pass a \ref std::reference_wrapper to allow to
   * modify the value after construction.
   **/
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  template <class T, class GridView>
  class ConstantGridFunction
  {
  public:
    using EntitySet = Dune::Functions::GridViewEntitySet<GridView, 0>;
    using Domain = typename EntitySet::GlobalCoordinate;
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    using Range = Underlying_t<T>;

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    enum { hasDerivative = false };

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  private:
    using Element = typename EntitySet::Element;
    using LocalDomain = typename EntitySet::LocalCoordinate;
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    using LocalFunction = ConstantLocalFunction<Range(LocalDomain), Element, T>;
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  public:
    /// Constructor. Stores the function `fct` and creates an `EntitySet`.
    ConstantGridFunction(T const& value, GridView const& gridView)
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      : value_(value)
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      , entitySet_(gridView)
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    {}

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    /// Return the constant `value_`
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    Range const& operator()(Domain const& /*x*/) const
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    {
      return value_;
    }

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    EntitySet const& entitySet() const
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    {
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      return entitySet_;
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    }

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    /// \brief Create an \ref ConstantLocalFunction with the stores `value_`.
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    LocalFunction localFunction() const
    {
      return {value_};
    }
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  private:
    T value_;
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    EntitySet entitySet_;
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  };

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  /// \relates ConstantGridFunction
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  template <class T, class GV>
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  auto localFunction(ConstantGridFunction<T,GV> const& gf)
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  {
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    return gf.localFunction();
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  }

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  namespace Concepts
  {
    /** \addtogroup Concepts
     *  @{
     **/

    namespace Definition
    {
      template <class T>
      struct ConstantToGridFunction
        : std::is_arithmetic<T> {};

      template <class T>
      struct ConstantToGridFunction<std::reference_wrapper<T>>
        : ConstantToGridFunction<T> {};

      template <class T, int N>
      struct ConstantToGridFunction<Dune::FieldVector<T, N>>
        : ConstantToGridFunction<T> {};

      template <class T, int N, int M>
      struct ConstantToGridFunction<Dune::FieldMatrix<T, N, M>>
        : ConstantToGridFunction<T> {};

      template <class T, int N>
      struct ConstantToGridFunction<Dune::DiagonalMatrix<T, N>>
        : ConstantToGridFunction<T> {};

    } // end namespace Definition


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    /// \brief Concepts that is true for all ''simple'' types that can be
    /// converted automatically to a GridFunction, e.g. arithmetic types,
    /// FieldVectors, and `std::reference_wrapper`.
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    template <class T>
    constexpr bool ConstantToGridFunction =
      Definition::ConstantToGridFunction<T>::value;

    /** @} **/

  } // end namespace Concepts

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  template <class Value>
  struct GridFunctionCreator<Value, std::enable_if_t<Concepts::ConstantToGridFunction<Value>>>
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  {
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    template <class GridView>
    static auto create(Value const& value, GridView const& gridView)
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    {
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      return ConstantGridFunction<Value,GridView>{value, gridView};
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    }
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  };
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} // end namespace AMDiS