discretization/cellcentered/mpfa/fvgridgeometry.hh

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#ifndef DUMUX_DISCRETIZATION_CC_MPFA_FV_GRID_GEOMETRY_HH
#define DUMUX_DISCRETIZATION_CC_MPFA_FV_GRID_GEOMETRY_HH
 
#include <utility>
 
#include <dumux/common/parameters.hh>
#include <dumux/common/indextraits.hh>
#include <dumux/discretization/method.hh>
#include <dumux/discretization/extrusion.hh>
#include <dumux/discretization/basegridgeometry.hh>
#include <dumux/discretization/checkoverlapsize.hh>
 
namespace Dumux {

template<class GridView, class Traits, bool enableCache>
class CCMpfaFVGridGeometry;

template<class GridView>
void checkOverlapSizeCCMpfa(const GridView& gridView)
{
    // Check if the overlap size is what we expect
    if (!CheckOverlapSize<DiscretizationMethods::CCMpfa>::isValid(gridView))
        DUNE_THROW(Dune::InvalidStateException, "The ccmpfa discretization method needs at least an overlap of 1 for parallel computations. "
                                                 << " Set the parameter \"Grid.Overlap\" in the input file.");
}

template<class GV, class Traits>
class CCMpfaFVGridGeometry<GV, Traits, true>
: public BaseGridGeometry<GV, Traits>
{
    using ThisType = CCMpfaFVGridGeometry<GV, Traits, true>;
    using ParentType = BaseGridGeometry<GV, Traits>;
 
    static constexpr int dim = GV::dimension;
    static constexpr int dimWorld = GV::dimensionworld;
 
    using Element = typename GV::template Codim<0>::Entity;
    using Vertex = typename GV::template Codim<dim>::Entity;
    using Intersection = typename GV::Intersection;
    using GridIndexType = typename IndexTraits<GV>::GridIndex;
    using CoordScalar = typename GV::ctype;
 
    using ScvfOutsideGridIndexStorage = typename Traits::SubControlVolumeFace::Traits::OutsideGridIndexStorage;
 
public:
    using FlipScvfIndexSet = std::vector<ScvfOutsideGridIndexStorage>;
    using GridIVIndexSets = typename Traits::template GridIvIndexSets<ThisType>;
    using SecondaryIvIndicatorType = std::function<bool(const Element&, const Intersection&, bool)>;

    using LocalView = typename Traits::template LocalView<ThisType, true>;
    using SubControlVolume = typename Traits::SubControlVolume;
    using SubControlVolumeFace = typename Traits::SubControlVolumeFace;
    using Extrusion = Extrusion_t<Traits>;
    using ConnectivityMap = typename Traits::template ConnectivityMap<ThisType>;
    using DofMapper = typename Traits::ElementMapper;
    using GridView = GV;
    using MpfaHelper = typename Traits::template MpfaHelper<ThisType>;

    using DiscretizationMethod = DiscretizationMethods::CCMpfa;
    static constexpr DiscretizationMethod discMethod{};

    static constexpr int maxElementStencilSize = Traits::maxElementStencilSize;

    static constexpr bool hasSingleInteractionVolumeType = !MpfaHelper::considerSecondaryIVs();

    CCMpfaFVGridGeometry(const GridView& gridView)
    : ParentType(gridView)
    , secondaryIvIndicator_([] (const Element& e, const Intersection& is, bool isBranching)
                               { return is.boundary() || isBranching; } )
    {
        checkOverlapSizeCCMpfa(gridView);
        update_();
    }

    CCMpfaFVGridGeometry(const GridView& gridView, const SecondaryIvIndicatorType& indicator)
    : ParentType(gridView)
    , secondaryIvIndicator_(indicator)
    {
        checkOverlapSizeCCMpfa(gridView);
        update_();
    }

    const DofMapper& dofMapper() const
    { return this->elementMapper(); }

    std::size_t numScv() const
    { return scvs_.size(); }

    std::size_t numScvf() const
    { return scvfs_.size(); }

    std::size_t numBoundaryScvf() const
    { return numBoundaryScvf_; }

    std::size_t numDofs() const
    { return this->gridView().size(0); }

    template<bool useSecondary = !hasSingleInteractionVolumeType, std::enable_if_t<useSecondary, bool> = 0>
    bool vertexUsesSecondaryInteractionVolume(GridIndexType vIdxGlobal) const
    { return secondaryInteractionVolumeVertices_[vIdxGlobal]; }

    template<bool useSecondary = !hasSingleInteractionVolumeType, std::enable_if_t<!useSecondary, bool> = 0>
    constexpr bool vertexUsesSecondaryInteractionVolume(GridIndexType vIdxGlobal) const
    { return false; }
 

    void update(const GridView& gridView)
    {
        ParentType::update(gridView);
        update_();
    }

    void update(GridView&& gridView)
    {
        ParentType::update(std::move(gridView));
        update_();
    }

    MpfaHelper mpfaHelper() const
    { return MpfaHelper(); }

    const SubControlVolume& scv(GridIndexType scvIdx) const
    { return scvs_[scvIdx]; }

    const SubControlVolumeFace& scvf(GridIndexType scvfIdx) const
    { return scvfs_[scvfIdx]; }

    const ConnectivityMap& connectivityMap() const
    { return connectivityMap_; }

    const GridIVIndexSets& gridInteractionVolumeIndexSets() const
    { return ivIndexSets_; }

    const std::vector<GridIndexType>& scvfIndicesOfScv(GridIndexType scvIdx) const
    { return scvfIndicesOfScv_[scvIdx]; }

    const FlipScvfIndexSet& flipScvfIndexSet() const
    { return flipScvfIndices_; }

    const SubControlVolumeFace& flipScvf(GridIndexType scvfIdx, unsigned int outsideScvfIdx = 0) const
    { return scvfs_[flipScvfIndices_[scvfIdx][outsideScvfIdx]]; }

    bool hasBoundaryScvf(GridIndexType eIdx) const
    { return hasBoundaryScvf_[eIdx]; }
 
private:
 
    void update_()
    {
        // stop the time required for the update
        Dune::Timer timer;
 
        // clear scvfs container
        scvfs_.clear();
 
        // determine the number of geometric entities
        const auto numVert = this->gridView().size(dim);
        const auto numScvs = numDofs();
        std::size_t numScvf = MpfaHelper::getGlobalNumScvf(this->gridView());
 
        // resize containers
        scvs_.resize(numScvs);
        scvfs_.reserve(numScvf);
        scvfIndicesOfScv_.resize(numScvs);
        hasBoundaryScvf_.assign(numScvs, false);
 
        // Some methods require to use a second type of interaction volume, e.g.
        // around vertices on the boundary or branching points (surface grids)
        secondaryInteractionVolumeVertices_.assign(numVert, false);
 
        // find vertices on processor boundaries
        const auto isGhostVertex = MpfaHelper::findGhostVertices(this->gridView(), this->vertexMapper());
 
        // instantiate the dual grid index set (to be used for construction of interaction volumes)
        typename GridIVIndexSets::DualGridIndexSet dualIdSet(this->gridView());
 
        // Build the SCVs and SCV faces
        GridIndexType scvfIdx = 0;
        numBoundaryScvf_ = 0;
        for (const auto& element : elements(this->gridView()))
        {
            const auto eIdx = this->elementMapper().index(element);
 
            // the element geometry
            auto elementGeometry = element.geometry();
 
            // The local scvf index set
            std::vector<GridIndexType> scvfIndexSet;
            scvfIndexSet.reserve(MpfaHelper::getNumLocalScvfs(elementGeometry.type()));
 
            // for network grids there might be multiple intersection with the same geometryInInside
            // we identify those by the indexInInside for now (assumes conforming grids at branching facets)
            std::vector<ScvfOutsideGridIndexStorage> outsideIndices;
            if (dim < dimWorld)
            {
                outsideIndices.resize(element.subEntities(1));
                for (const auto& intersection : intersections(this->gridView(), element))
                {
                    if (intersection.neighbor())
                    {
                        const auto nIdx = this->elementMapper().index( intersection.outside() );
                        outsideIndices[intersection.indexInInside()].push_back(nIdx);
                    }
                }
            }
 
            // construct the sub control volume faces
            for (const auto& is : intersections(this->gridView(), element))
            {
                const auto indexInInside = is.indexInInside();
                const bool boundary = is.boundary();
                const bool neighbor = is.neighbor();
 
                if (boundary)
                    hasBoundaryScvf_[eIdx] = true;
 
                // for surface grids, skip the rest if handled already
                if (dim < dimWorld && neighbor && outsideIndices[indexInInside].empty())
                    continue;
 
                // if outside level > inside level, use the outside element in the following
                const bool useNeighbor = neighbor && is.outside().level() > element.level();
                const auto& e = useNeighbor ? is.outside() : element;
                const auto indexInElement = useNeighbor ? is.indexInOutside() : indexInInside;
                const auto eg = e.geometry();
                const auto refElement = referenceElement(eg);
 
                // Set up a container with all relevant positions for scvf corner computation
                const auto numCorners = is.geometry().corners();
                const auto isPositions = MpfaHelper::computeScvfCornersOnIntersection(eg,
                                                                                      refElement,
                                                                                      indexInElement,
                                                                                      numCorners);
 
                // evaluate if vertices on this intersection use primary/secondary IVs
                const bool isBranchingPoint = dim < dimWorld ? outsideIndices[indexInInside].size() > 1 : false;
                const bool usesSecondaryIV = secondaryIvIndicator_(element, is, isBranchingPoint);
 
                // make the scv faces belonging to each corner of the intersection
                for (std::size_t c = 0; c < numCorners; ++c)
                {
                    // get the global vertex index the scv face is connected to
                    const auto vIdxLocal = refElement.subEntity(indexInElement, 1, c, dim);
                    const auto vIdxGlobal = this->vertexMapper().subIndex(e, vIdxLocal, dim);
 
                    // do not build scvfs connected to a processor boundary
                    if (isGhostVertex[vIdxGlobal])
                        continue;
 
                    // if this vertex is tagged to use the secondary IVs, store info
                    if (usesSecondaryIV)
                        secondaryInteractionVolumeVertices_[vIdxGlobal] = true;
 
                    // the quadrature point parameterizarion to be used on scvfs
                    static const auto q = getParam<CoordScalar>("MPFA.Q");
 
                    // make the scv face (for non-boundary scvfs on network grids, use precalculated outside indices)
                    const auto& outsideScvIndices = [&] ()
                                                    {
                                                        if (!boundary)
                                                            return dim == dimWorld ?
                                                                   ScvfOutsideGridIndexStorage({this->elementMapper().index(is.outside())}) :
                                                                   outsideIndices[indexInInside];
                                                        else
                                                            return ScvfOutsideGridIndexStorage({GridIndexType(numScvs) + numBoundaryScvf_++});
                                                    } ();
 
                    scvfIndexSet.push_back(scvfIdx);
                    scvfs_.emplace_back(MpfaHelper(),
                                        MpfaHelper::getScvfCorners(isPositions, numCorners, c),
                                        is,
                                        vIdxGlobal,
                                        vIdxLocal,
                                        scvfIdx,
                                        eIdx,
                                        outsideScvIndices,
                                        q,
                                        boundary);
 
                    // insert the scvf data into the dual grid index set
                    dualIdSet[vIdxGlobal].insert(scvfs_.back());
 
                    // increment scvf counter
                    scvfIdx++;
                }
 
                // for network grids, clear outside indices to not make a second scvf on that facet
                if (dim < dimWorld)
                    outsideIndices[indexInInside].clear();
            }
 
            // create sub control volume for this element
            scvs_[eIdx] = SubControlVolume(std::move(elementGeometry), eIdx);
 
            // Save the scvf indices belonging to this scv to build up fv element geometries fast
            scvfIndicesOfScv_[eIdx] = scvfIndexSet;
        }
 
        // Make the flip index set for network and surface grids
        flipScvfIndices_.resize(scvfs_.size());
        for (const auto& scvf : scvfs_)
        {
            if (scvf.boundary())
                continue;
 
            const auto numOutsideScvs = scvf.numOutsideScvs();
            const auto vIdxGlobal = scvf.vertexIndex();
            const auto insideScvIdx = scvf.insideScvIdx();
 
            flipScvfIndices_[scvf.index()].resize(numOutsideScvs);
            for (std::size_t i = 0; i < numOutsideScvs; ++i)
            {
                const auto outsideScvIdx = scvf.outsideScvIdx(i);
                for (auto outsideScvfIndex : scvfIndicesOfScv_[outsideScvIdx])
                {
                    const auto& outsideScvf = this->scvf(outsideScvfIndex);
                    if (outsideScvf.vertexIndex() == vIdxGlobal &&
                        MpfaHelper::vectorContainsValue(outsideScvf.outsideScvIndices(), insideScvIdx))
                    {
                        flipScvfIndices_[scvf.index()][i] = outsideScvfIndex;
                        // there is always only one flip face in an outside element
                        break;
                    }
                }
            }
        }
 
        // building the geometries has finished
        std::cout << "Initializing of the grid finite volume geometry took " << timer.elapsed() << " seconds." << std::endl;
 
        // Initialize the grid interaction volume index sets
        timer.reset();
        ivIndexSets_.update(*this, std::move(dualIdSet));
        std::cout << "Initializing of the grid interaction volume index sets took " << timer.elapsed() << " seconds." << std::endl;
 
        // build the connectivity map for an efficient assembly
        timer.reset();
        connectivityMap_.update(*this);
        std::cout << "Initializing of the connectivity map took " << timer.elapsed() << " seconds." << std::endl;
    }
 
    // connectivity map for efficient assembly
    ConnectivityMap connectivityMap_;
 
    // the finite volume grid geometries
    std::vector<SubControlVolume> scvs_;
    std::vector<SubControlVolumeFace> scvfs_;
 
    // containers storing the global data
    std::vector<std::vector<GridIndexType>> scvfIndicesOfScv_;
    std::vector<bool> secondaryInteractionVolumeVertices_;
    GridIndexType numBoundaryScvf_;
    std::vector<bool> hasBoundaryScvf_;
 
    // needed for embedded surface and network grids (dim < dimWorld)
    FlipScvfIndexSet flipScvfIndices_;
 
    // The grid interaction volume index set
    GridIVIndexSets ivIndexSets_;
 
    // Indicator function on where to use the secondary IVs
    SecondaryIvIndicatorType secondaryIvIndicator_;
};

template<class GV, class Traits>
class CCMpfaFVGridGeometry<GV, Traits, false>
: public BaseGridGeometry<GV, Traits>
{
    using ThisType = CCMpfaFVGridGeometry<GV, Traits, false>;
    using ParentType = BaseGridGeometry<GV, Traits>;
 
    static constexpr int dim = GV::dimension;
    static constexpr int dimWorld = GV::dimensionworld;
 
    using Element = typename GV::template Codim<0>::Entity;
    using Vertex = typename GV::template Codim<dim>::Entity;
    using Intersection = typename GV::Intersection;
    using GridIndexType = typename IndexTraits<GV>::GridIndex;
    using CoordScalar = typename GV::ctype;
 
    using ScvfOutsideGridIndexStorage = typename Traits::SubControlVolumeFace::Traits::OutsideGridIndexStorage;
 
public:
    using FlipScvfIndexSet = std::vector<ScvfOutsideGridIndexStorage>;
    using GridIVIndexSets = typename Traits::template GridIvIndexSets<ThisType>;
    using SecondaryIvIndicatorType = std::function<bool(const Element&, const Intersection&, bool)>;

    using LocalView = typename Traits::template LocalView<ThisType, false>;
    using SubControlVolume = typename Traits::SubControlVolume;
    using SubControlVolumeFace = typename Traits::SubControlVolumeFace;
    using Extrusion = Extrusion_t<Traits>;
    using ConnectivityMap = typename Traits::template ConnectivityMap<ThisType>;
    using DofMapper = typename Traits::ElementMapper;
    using GridView = GV;
    using MpfaHelper = typename Traits::template MpfaHelper<ThisType>;

    using DiscretizationMethod = DiscretizationMethods::CCMpfa;
    static constexpr DiscretizationMethod discMethod{};

    static constexpr int maxElementStencilSize = Traits::maxElementStencilSize;

    static constexpr bool hasSingleInteractionVolumeType = !MpfaHelper::considerSecondaryIVs();

    CCMpfaFVGridGeometry(const GridView& gridView)
    : ParentType(gridView)
    , secondaryIvIndicator_([] (const Element& e, const Intersection& is, bool isBranching)
                               { return is.boundary() || isBranching; } )
    {
        checkOverlapSizeCCMpfa(gridView);
        update_();
    }

    CCMpfaFVGridGeometry(const GridView& gridView, const SecondaryIvIndicatorType& indicator)
    : ParentType(gridView)
    , secondaryIvIndicator_(indicator)
    {
        checkOverlapSizeCCMpfa(gridView);
        update_();
    }

    const DofMapper& dofMapper() const
    { return this->elementMapper(); }

    std::size_t numScv() const
    { return numScvs_; }

    std::size_t numScvf() const
    { return numScvf_; }

    std::size_t numBoundaryScvf() const
    { return numBoundaryScvf_; }

    std::size_t numDofs() const
    { return this->gridView().size(0); }

    template<bool useSecondary = !hasSingleInteractionVolumeType, std::enable_if_t<useSecondary, bool> = 0>
    bool vertexUsesSecondaryInteractionVolume(GridIndexType vIdxGlobal) const
    { return secondaryInteractionVolumeVertices_[vIdxGlobal]; }

    template<bool useSecondary = !hasSingleInteractionVolumeType, std::enable_if_t<!useSecondary, bool> = 0>
    constexpr bool vertexUsesSecondaryInteractionVolume(GridIndexType vIdxGlobal) const
    { return false; }

    bool isGhostVertex(const Vertex& v) const
    { return isGhostVertex_[this->vertexMapper().index(v)]; }

    bool isGhostVertex(GridIndexType vIdxGlobal) const
    { return isGhostVertex_[vIdxGlobal]; }
 

    void update(const GridView& gridView)
    {
        ParentType::update(gridView);
        update_();
    }

    void update(GridView&& gridView)
    {
        ParentType::update(std::move(gridView));
        update_();
    }

    MpfaHelper mpfaHelper() const
    { return MpfaHelper(); }

    const std::vector<GridIndexType>& scvfIndicesOfScv(GridIndexType scvIdx) const
    { return scvfIndicesOfScv_[scvIdx]; }

    const std::vector<ScvfOutsideGridIndexStorage>& neighborVolVarIndices(GridIndexType scvIdx) const
    { return neighborVolVarIndices_[scvIdx]; }

    const GridIndexType flipScvfIdx(GridIndexType scvfIdx, unsigned int outsideScvfIdx = 0) const
    { return flipScvfIndices_[scvfIdx][outsideScvfIdx]; }

    const FlipScvfIndexSet& flipScvfIndexSet() const
    { return flipScvfIndices_; }

    const ConnectivityMap& connectivityMap() const
    { return connectivityMap_; }

    const GridIVIndexSets& gridInteractionVolumeIndexSets() const
    { return ivIndexSets_; }
 
private:
 
    void update_()
    {
 
        // stop the time required for the update
        Dune::Timer timer;
 
        // resize containers
        numScvs_ = numDofs();
        scvfIndicesOfScv_.resize(numScvs_);
        neighborVolVarIndices_.resize(numScvs_);
 
        // Some methods require to use a second type of interaction volume, e.g.
        // around vertices on the boundary or branching points (surface grids)
        const auto numVert = this->gridView().size(dim);
        secondaryInteractionVolumeVertices_.assign(numVert, false);
 
        // find vertices on processor boundaries HERE!!
        isGhostVertex_ = MpfaHelper::findGhostVertices(this->gridView(), this->vertexMapper());
 
        // instantiate the dual grid index set (to be used for construction of interaction volumes)
        typename GridIVIndexSets::DualGridIndexSet dualIdSet(this->gridView());
 
        // keep track of boundary scvfs and scvf vertex indices in order to set up flip scvf index set
        const auto maxNumScvfs = numScvs_*LocalView::maxNumElementScvfs;
        std::vector<bool> scvfIsOnBoundary;
        std::vector<GridIndexType> scvfVertexIndex;
        scvfIsOnBoundary.reserve(maxNumScvfs);
        scvfVertexIndex.reserve(maxNumScvfs);
 
        // Build the SCVs and SCV faces
        numScvf_ = 0;
        numBoundaryScvf_ = 0;
        for (const auto& element : elements(this->gridView()))
        {
            const auto eIdx = this->elementMapper().index(element);
 
            // the element geometry
            auto elementGeometry = element.geometry();
 
            // the element-wise index sets for finite volume geometry
            const auto numLocalFaces = MpfaHelper::getNumLocalScvfs(elementGeometry.type());
            std::vector<GridIndexType> scvfsIndexSet;
            std::vector<ScvfOutsideGridIndexStorage> neighborVolVarIndexSet;
            scvfsIndexSet.reserve(numLocalFaces);
            neighborVolVarIndexSet.reserve(numLocalFaces);
 
            // for network grids there might be multiple intersections with the same geometryInInside
            // we identify those by the indexInInside for now (assumes conforming grids at branching facets)
            std::vector<ScvfOutsideGridIndexStorage> outsideIndices;
            if (dim < dimWorld)
            {
                outsideIndices.resize(element.subEntities(1));
                for (const auto& intersection : intersections(this->gridView(), element))
                {
                    if (intersection.neighbor())
                    {
                        auto nIdx = this->elementMapper().index( intersection.outside() );
                        outsideIndices[intersection.indexInInside()].push_back(nIdx);
                    }
                }
            }
 
            // construct the sub control volume faces
            for (const auto& is : intersections(this->gridView(), element))
            {
                const auto indexInInside = is.indexInInside();
                const bool boundary = is.boundary();
                const bool neighbor = is.neighbor();
 
                // for surface grids, skip the rest if handled already
                if (dim < dimWorld && neighbor && outsideIndices[indexInInside].empty())
                    continue;
 
                // if outside level > inside level, use the outside element in the following
                const bool useNeighbor = neighbor && is.outside().level() > element.level();
                const auto& e = useNeighbor ? is.outside() : element;
                const auto indexInElement = useNeighbor ? is.indexInOutside() : indexInInside;
                const auto eg = e.geometry();
                const auto refElement = referenceElement(eg);
 
                // evaluate if vertices on this intersection use primary/secondary IVs
                const bool isBranchingPoint = dim < dimWorld ? outsideIndices[indexInInside].size() > 1 : false;
                const bool usesSecondaryIV = secondaryIvIndicator_(element, is, isBranchingPoint);
 
                // make the scv faces belonging to each corner of the intersection
                for (std::size_t c = 0; c < is.geometry().corners(); ++c)
                {
                    // get the global vertex index the scv face is connected to
                    const auto vIdxLocal = refElement.subEntity(indexInElement, 1, c, dim);
                    const auto vIdxGlobal = this->vertexMapper().subIndex(e, vIdxLocal, dim);
 
                    // do not build scvfs connected to a processor boundary
                    if (isGhostVertex_[vIdxGlobal])
                        continue;
 
                    // if this vertex is tagged to use the secondary IVs, store info
                    if (usesSecondaryIV)
                        secondaryInteractionVolumeVertices_[vIdxGlobal] = true;
 
                    // make the scv face (for non-boundary scvfs on network grids, use precalculated outside indices)
                    const auto& outsideScvIndices = [&] ()
                                                    {
                                                        if (!boundary)
                                                            return dim == dimWorld ?
                                                                   ScvfOutsideGridIndexStorage({this->elementMapper().index(is.outside())}) :
                                                                   outsideIndices[indexInInside];
                                                        else
                                                            return ScvfOutsideGridIndexStorage({GridIndexType(numScvs_) + numBoundaryScvf_++});
                                                    } ();
 
                    // insert the scvf data into the dual grid index set
                    dualIdSet[vIdxGlobal].insert(numScvf_, eIdx, boundary);
 
                    // store information on the scv face
                    scvfsIndexSet.push_back(numScvf_++);
                    scvfIsOnBoundary.push_back(boundary);
                    scvfVertexIndex.push_back(vIdxGlobal);
                    neighborVolVarIndexSet.emplace_back(std::move(outsideScvIndices));
                }
 
                // for network grids, clear outside indices to not make a second scvf on that facet
                if (dim < dimWorld)
                    outsideIndices[indexInInside].clear();
            }
 
            // store the sets of indices in the data container
            scvfIndicesOfScv_[eIdx] = scvfsIndexSet;
            neighborVolVarIndices_[eIdx] = neighborVolVarIndexSet;
        }
 
        // Make the flip scvf index set
        flipScvfIndices_.resize(numScvf_);
        for (std::size_t scvIdx = 0; scvIdx < numScvs_; ++scvIdx)
        {
            const auto& scvfIndices = scvfIndicesOfScv_[scvIdx];
            for (unsigned int i = 0; i < scvfIndices.size(); ++i)
            {
                // boundary scvf have no flip scvfs
                if (scvfIsOnBoundary[ scvfIndices[i] ])
                    continue;
 
                const auto scvfIdx = scvfIndices[i];
                const auto vIdxGlobal = scvfVertexIndex[scvfIdx];
                const auto numOutsideScvs = neighborVolVarIndices_[scvIdx][i].size();
 
                flipScvfIndices_[scvfIdx].resize(numOutsideScvs);
                for (unsigned int j = 0; j < numOutsideScvs; ++j)
                {
                    const auto outsideScvIdx = neighborVolVarIndices_[scvIdx][i][j];
                    const auto& outsideScvfIndices = scvfIndicesOfScv_[outsideScvIdx];
                    for (unsigned int k = 0; k < outsideScvfIndices.size(); ++k)
                    {
                        const auto outsideScvfIndex = outsideScvfIndices[k];
                        const auto outsideScvfVertexIndex = scvfVertexIndex[outsideScvfIndex];
                        const auto& outsideScvfNeighborIndices = neighborVolVarIndices_[outsideScvIdx][k];
                        if (outsideScvfVertexIndex == vIdxGlobal &&
                            MpfaHelper::vectorContainsValue(outsideScvfNeighborIndices, scvIdx))
                        {
                            flipScvfIndices_[scvfIdx][j] = outsideScvfIndex;
                            // there is always only one flip face in an outside element
                            break;
                        }
                    }
                }
            }
        }
 
        // building the geometries has finished
        std::cout << "Initializing of the grid finite volume geometry took " << timer.elapsed() << " seconds." << std::endl;
 
        // Initialize the grid interaction volume index sets
        timer.reset();
        ivIndexSets_.update(*this, std::move(dualIdSet));
        std::cout << "Initializing of the grid interaction volume index sets took " << timer.elapsed() << " seconds." << std::endl;
 
        // build the connectivity map for an efficient assembly
        timer.reset();
        connectivityMap_.update(*this);
        std::cout << "Initializing of the connectivity map took " << timer.elapsed() << " seconds." << std::endl;
    }
 
    // connectivity map for efficient assembly
    ConnectivityMap connectivityMap_;
 
    // containers storing the global data
    std::vector<std::vector<GridIndexType>> scvfIndicesOfScv_;
    std::vector<std::vector<ScvfOutsideGridIndexStorage>> neighborVolVarIndices_;
    std::vector<bool> secondaryInteractionVolumeVertices_;
    std::vector<bool> isGhostVertex_;
    GridIndexType numScvs_;
    GridIndexType numScvf_;
    GridIndexType numBoundaryScvf_;
 
    // needed for embedded surface and network grids (dim < dimWorld)
    FlipScvfIndexSet flipScvfIndices_;
 
    // The grid interaction volume index set
    GridIVIndexSets ivIndexSets_;
 
    // Indicator function on where to use the secondary IVs
    SecondaryIvIndicatorType secondaryIvIndicator_;
};
 
} // end namespace Dumux
 
#endif