coarsefunctiononfinegridview.hh

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// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
 
// SPDX-FileCopyrightText: Copyright © DUNE Project contributors, see file AUTHORS.md
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception OR LGPL-3.0-or-later
 
#ifndef DUNE_FUNCTIONS_GRIDFUNCTIONS_COARSEFUNCTIONONFINEGRIDVIEW_HH
#define DUNE_FUNCTIONS_GRIDFUNCTIONS_COARSEFUNCTIONONFINEGRIDVIEW_HH
 
#include <optional>
#include <type_traits>
#include <utility>
 
#include <dune/common/referencehelper.hh>
 
#include <dune/functions/common/defaultderivativetraits.hh>
#include <dune/functions/common/geometryinancestor.hh>
#include <dune/functions/gridfunctions/gridfunction.hh>
#include <dune/functions/gridfunctions/gridviewentityset.hh>
 
namespace Dune::Functions {
 
 

template<class GridFunction, class GV, template<class> class DerivativeTraits=Dune::Functions::DefaultDerivativeTraits>
class CoarseFunctionOnFineGridView
{
  using RawGridFunction = Dune::ResolveRef_t<GridFunction>;
 
  auto&& rawFunction() const
  {
    return Dune::resolveRef(function_);
  }
 
public:
 
  using GridView = GV;
  using EntitySet = Dune::Functions::GridViewEntitySet<GridView, 0>;
  using Element = typename EntitySet::Element;
  using Domain = typename EntitySet::GlobalCoordinate;
  using LocalDomain = typename EntitySet::LocalCoordinate;
  using Range = std::decay_t<decltype(std::declval<RawGridFunction>()(std::declval<Domain>()))>;
 
private:
 
  using CoarseEntitySet = std::decay_t<decltype(std::declval<RawGridFunction>().entitySet())>;
  using GeometryInAncestor = Dune::Functions::GeometryInAncestor<Element>;
  using Traits = Dune::Functions::Imp::GridFunctionTraits<Range(Domain), EntitySet, DerivativeTraits, 56>;
 
  class CoarseLocalFunctionOnFineGridView
  {
    using Traits = typename CoarseFunctionOnFineGridView::Traits::LocalFunctionTraits;
 
  public:
 
    using Derivative = decltype(localFunction(derivative(std::declval<CoarseFunctionOnFineGridView>())));
    using RawLocalFunction = std::decay_t<decltype(localFunction(std::declval<const RawGridFunction&>()))>;

    CoarseLocalFunctionOnFineGridView(RawLocalFunction&& localFunction, const CoarseEntitySet& coarseEntitySet)
      : element_()
      , localFunction_(localFunction)
      , coarseEntitySet_(coarseEntitySet)
      , geometryInAncestor_()
    {}

    CoarseLocalFunctionOnFineGridView(
        RawLocalFunction&& localFunction,
        const CoarseEntitySet& coarseEntitySet,
        const GeometryInAncestor& geometryInAncestor,
        const std::optional<Element>& element
      )
      : element_(element)
      , localFunction_(localFunction)
      , coarseEntitySet_(coarseEntitySet)
      , geometryInAncestor_(geometryInAncestor, *element_)
    {}

    void bind(const Element& element)
    {
      element_ = element;
      geometryInAncestor_.bind(*element_, [&](const auto& e) { return not coarseEntitySet_.contains(e); });
      localFunction_.bind(geometryInAncestor_.coarseElement());
    }

    void unbind()
    {
      element_.reset();
    }

    bool bound() const
    {
      return static_cast<bool>(element_);
    }

    const Element& localContext() const
    {
      return *element_;
    }

    friend auto derivative(const CoarseLocalFunctionOnFineGridView& f)
    {
      if constexpr(requires{ derivative(f.localFunction_); })
        return Derivative(derivative(f.localFunction_), f.coarseEntitySet_, f.geometryInAncestor_, f.element_);
      else
        return typename Traits::DerivativeInterface{};
    }

    Range operator()(LocalDomain x) const
    {
      return localFunction_(geometryInAncestor_.global(x));
    }
 
  private:
    std::optional<Element> element_;
    RawLocalFunction localFunction_;
    const CoarseEntitySet& coarseEntitySet_;
    GeometryInAncestor geometryInAncestor_;
  };
 
public:
 
  using LocalFunction = CoarseLocalFunctionOnFineGridView;

  CoarseFunctionOnFineGridView(const GridFunction& function, const GridView& gridView)
    : function_(function)
    , entitySet_(gridView)
  {}

  CoarseFunctionOnFineGridView(GridFunction&& function, const GridView& gridView)
    : function_(std::move(function))
    , entitySet_(gridView)
  {}

  Range operator()(const Domain& x) const
  {
    return function_(x);
  }

  friend auto derivative(const CoarseFunctionOnFineGridView& f)
  {
    if constexpr(requires{ derivative(f.rawFunction()); })
    {
      using RawDerivative = std::decay_t<decltype(derivative(f.rawFunction()))>;
      return CoarseFunctionOnFineGridView<RawDerivative, GridView, DerivativeTraits>(derivative(f.rawFunction()), f.entitySet_.gridView());
    }
    else
      return typename Traits::DerivativeInterface{};
  }

  friend LocalFunction localFunction(const CoarseFunctionOnFineGridView& f)
  {
    return LocalFunction(localFunction(f.rawFunction()), f.rawFunction().entitySet());
  }

  const EntitySet& entitySet() const
  {
    return entitySet_;
  }
 
protected:
 
  GridFunction function_;
  EntitySet entitySet_;
};
 
 
 
} // namespace Dune::Functions
 
#endif // DUNE_FUNCTIONS_GRIDFUNCTIONS_COARSEFUNCTIONONFINEGRIDVIEW_HH