dynamicpowerbasis.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_FUNCTIONSPACEBASES_DYNAMICPOWERBASIS_HH
#define DUNE_FUNCTIONS_FUNCTIONSPACEBASES_DYNAMICPOWERBASIS_HH
 
#include <dune/common/reservedvector.hh>
#include <dune/common/typeutilities.hh>
#include <dune/common/indices.hh>
 
#include <dune/common/typetree/nodeconcepts.hh>
 
#include <dune/functions/common/utility.hh>
#include <dune/functions/common/type_traits.hh>
#include <dune/functions/functionspacebases/basistags.hh>
#include <dune/functions/functionspacebases/containerdescriptors.hh>
#include <dune/functions/functionspacebases/nodes.hh>
#include <dune/functions/functionspacebases/concepts.hh>
 
 
 
namespace Dune {
namespace Functions {
 
 
// *****************************************************************************
// This is the reusable part of the dynamic power bases. It contains
//
//   DynamicPowerPreBasis
//
// The pre-basis allows to create the others and is the owner of possible shared
// state. These components do _not_ depend on the global basis and local view
// and can be used without a global basis.
// *****************************************************************************

template<class IMS, class SPB>
class DynamicPowerPreBasis
{
  static const bool isBlocked = std::is_same_v<IMS,BasisFactory::BlockedLexicographic> or std::is_same_v<IMS,BasisFactory::BlockedInterleaved>;
 
public:

  using SubPreBasis = SPB;

  using GridView = typename SPB::GridView;

  using size_type = std::size_t;

  using IndexMergingStrategy = IMS;

  using Node = DynamicPowerBasisNode<typename SubPreBasis::Node>;
 
  static constexpr size_type maxMultiIndexSize = SubPreBasis::maxMultiIndexSize + isBlocked;
  static constexpr size_type minMultiIndexSize = SubPreBasis::minMultiIndexSize + isBlocked;
  static constexpr size_type multiIndexBufferSize = SubPreBasis::multiIndexBufferSize + isBlocked;

  template<class... SFArgs,
    disableCopyMove<DynamicPowerPreBasis, SFArgs...> = 0,
    enableIfConstructible<SubPreBasis, SFArgs...> = 0>
  explicit DynamicPowerPreBasis(std::size_t c, SFArgs&&... sfArgs) :
    children_(c),
    subPreBasis_(std::forward<SFArgs>(sfArgs)...)
  {
    static_assert(models<Concept::PreBasis<GridView>, SubPreBasis>(), "Subprebasis passed to DynamicPowerPreBasis does not model the PreBasis concept.");
  }

  void initializeIndices()
  {
    subPreBasis_.initializeIndices();
  }

  const GridView& gridView() const
  {
    return subPreBasis_.gridView();
  }

  void update(const GridView& gv)
  {
    subPreBasis_.update(gv);
  }

  Node makeNode() const
  {
    auto node = Node{children_};
    for (std::size_t i=0; i<children_; ++i)
      node.setChild(i, subPreBasis_.makeNode());
    return node;
  }
 
  std::size_t children() const
  {
    return children_;
  }

  size_type size() const
  {
    return size(Dune::ReservedVector<size_type, multiIndexBufferSize>{});
  }

  template<class SizePrefix>
  size_type size(const SizePrefix& prefix) const
  {
    return sizeImpl(prefix, children_, IndexMergingStrategy{});
  }
 
protected:
 
  template<class SizePrefix, class Children>
  size_type sizeImpl(SizePrefix prefix, Children children, BasisFactory::FlatInterleaved) const
  {
    // The root index size is the root index size of a single subnode
    // multiplied by the number of subnodes, because we enumerate all
    // child indices in a row.
    if (prefix.size() == 0)
      return children*subPreBasis_.size();
 
    // The FlatInterleaved index merging strategy only changes the first
    // index digit. Hence, we have to reconstruct the corresponding digit
    // for the subtree and can then return the corresponding size of the subtree.
    prefix[0] = prefix[0] / children;
    return subPreBasis_.size(prefix);
  }
 
  template<class SizePrefix, class Children>
  size_type sizeImpl(SizePrefix prefix, Children children, BasisFactory::FlatLexicographic) const
  {
    // The size at the index tree root is the size of at the index tree
    // root of a single subnode multiplied by the number of subnodes,
    // because we enumerate all child indices in a row.
    if (prefix.size() == 0)
      return children*subPreBasis_.size();
 
    // The first prefix entry refers to one of the (root index size)
    // subindex trees. Hence, we have to first compute the corresponding
    // prefix entry for a single subnode subnode. Then we can append
    // the other prefix entries unmodified, because the index tree
    // looks the same after the first level.
 
    // The FlatLexicographic index merging strategy only changes the first
    // index digit. Hence, we have to reconstruct the corresponding digit
    // for the subtree and can then return the corresponding size of the subtree.
    prefix[0] = prefix[0] % subPreBasis_.size();
    return subPreBasis_.size(prefix);
  }
 
  template<class MultiIndex>
  static void multiIndexPopFront(MultiIndex& M)
  {
    for(std::size_t i=0; i<M.size()-1; ++i)
      M[i] = M[i+1];
    M.resize(M.size()-1);
  }
 
  template<class SizePrefix, class Children>
  size_type sizeImpl(SizePrefix prefix, Children children, BasisFactory::BlockedLexicographic) const
  {
    if (prefix.size() == 0)
      return children;
    multiIndexPopFront(prefix);
    return subPreBasis_.size(prefix);
  }
 
  template<class SizePrefix, class Children>
  size_type sizeImpl(SizePrefix prefix, Children children, BasisFactory::BlockedInterleaved) const
  {
    if (prefix.size() == 0)
      return subPreBasis_.size();
 
    // Remember last index, remove it and check if the remaining
    // prefix refers to a leaf in the subPreBasis index tree.
    // If yes, then the full prefix must also refer to a
    // leaf in the merged index tree. If not, then restore the full
    // prefix and proceed.
    auto tail = prefix.back();
    prefix.pop_back();
    if (subPreBasis_.size(prefix) == 0)
      return 0;
    prefix.push_back(tail);
 
    // Now check if the full prefix refers to a leaf in the subPreBasis
    // index tree.
    // If yes, then it has exactly 'children' appended children in the subtree.
    // If not, then the index tree looks the same in the merged subtree and we
    // can forward the result.
    auto subSize = subPreBasis_.size(prefix);
    if (subSize == 0)
      return children;
    return subSize;
  }
 
public:

  size_type dimension() const
  {
    return subPreBasis_.dimension() * children_;
  }

  size_type maxNodeSize() const
  {
    return subPreBasis_.maxNodeSize() * children_;
  }

  const SubPreBasis& subPreBasis() const
  {
    return subPreBasis_;
  }

  SubPreBasis& subPreBasis()
  {
    return subPreBasis_;
  }

  template<class NodeType, typename It>
  requires Dune::TypeTree::Concept::UniformInnerTreeNode<NodeType>
  It indices(const NodeType& node, It it) const
  {
    return indicesImpl(node, it, children_, IndexMergingStrategy{});
  }

  auto containerDescriptor() const
  {
    return containerDescriptorImpl(children_);
  }
 
protected:
 
  template<class NodeType, typename It, class Children>
  It indicesImpl(const NodeType& node, It multiIndices, Children children, BasisFactory::FlatInterleaved) const
  {
    using namespace Dune::Indices;
    size_type subTreeSize = node.child(_0).size();
    // Fill indices for first child at the beginning.
    auto next = subPreBasis().indices(node.child(_0), multiIndices);
    // Multiply first component of all indices for first child by
    // number of children to stretch the index range for interleaving.
    for (std::size_t i = 0; i<subTreeSize; ++i)
      multiIndices[i][0] *= children;
    for (std::size_t child = 1; child<children; ++child)
    {
      for (std::size_t i = 0; i<subTreeSize; ++i)
      {
        // Copy indices from first child for all other children
        // and shift them by child index to interleave indices.
        //    multiIndices[child*subTreeSize+i] = multiIndices[i];
        //    multiIndices[child*subTreeSize+i][0] = multiIndices[i][0]+child;
        (*next) = multiIndices[i];
        (*next)[0] = multiIndices[i][0]+child;
        ++next;
      }
    }
    return next;
  }
 
  template<class NodeType, typename It, class Children>
  It indicesImpl(const NodeType& node, It multiIndices, Children children, BasisFactory::FlatLexicographic) const
  {
    using namespace Dune::Indices;
    size_type subTreeSize = node.child(_0).size();
    size_type firstIndexEntrySize = subPreBasis().size();
    // Fill indices for first child at the beginning.
    auto next = subPreBasis().indices(node.child(_0), multiIndices);
    for (std::size_t child = 1; child<children_; ++child)
    {
      for (std::size_t i = 0; i<subTreeSize; ++i)
      {
        // Copy indices from first child for all other children
        // and shift them by suitable offset to get lexicographic indices.
        //     multiIndices[child*subTreeSize+i] = multiIndices[i];
        //     multiIndices[child*subTreeSize+i][0] += child*firstIndexEntrySize;
        (*next) = multiIndices[i];
        (*next)[0] += child*firstIndexEntrySize;
        ++next;
      }
    }
    return next;
  }
 
  template<class MultiIndex>
  static void multiIndexPushFront(MultiIndex& M, size_type M0)
  {
    M.resize(M.size()+1);
    for(std::size_t i=M.size()-1; i>0; --i)
      M[i] = M[i-1];
    M[0] = M0;
  }
 
  template<class NodeType, typename It, class Children>
  It indicesImpl(const NodeType& node, It multiIndices, Children children, BasisFactory::BlockedLexicographic) const
  {
    using namespace Dune::Indices;
    size_type subTreeSize = node.child(_0).size();
    // Fill indices for first child at the beginning.
    auto next = subPreBasis().indices(node.child(_0), multiIndices);
    // Insert 0 before first component of all indices for first child.
    for (std::size_t i = 0; i<subTreeSize; ++i)
      multiIndexPushFront(multiIndices[i], 0);
    for (std::size_t child = 1; child<children_; ++child)
    {
      for (std::size_t i = 0; i<subTreeSize; ++i)
      {
        // Copy indices from first child for all other children and overwrite
        // zero in first component as inserted above by child index.
        //     multiIndices[child*subTreeSize+i] = multiIndices[i];
        //     multiIndices[child*subTreeSize+i][0] = child;
        (*next) = multiIndices[i];
        (*next)[0] = child;
        ++next;
      }
    }
    return next;
  }
 
  template<class NodeType, typename It, class Children>
  It indicesImpl(const NodeType& node, It multiIndices, Children children, BasisFactory::BlockedInterleaved) const
  {
    using namespace Dune::Indices;
    size_type subTreeSize = node.child(_0).size();
    // Fill indices for first child at the beginning.
    auto next = subPreBasis().indices(node.child(_0), multiIndices);
    // Append 0 after last component of all indices for first child.
    for (std::size_t i = 0; i<subTreeSize; ++i)
      multiIndices[i].push_back(0);
    for (std::size_t child = 1; child<children_; ++child)
    {
      for (std::size_t i = 0; i<subTreeSize; ++i)
      {
        // Copy indices from first child for all other children and overwrite
        // zero in last component as appended above by child index.
        (*next) = multiIndices[i];
        (*next).back() = child;
        ++next;
      }
    }
    return next;
  }
 
  template<class Children>
  auto containerDescriptorImpl(Children children) const
  {
    auto subTree = Dune::Functions::containerDescriptor(subPreBasis_);
    if constexpr(std::is_same_v<IMS, BasisFactory::FlatInterleaved>)
      return ContainerDescriptors::Impl::flatInterleavedN(children,std::move(subTree));
    else if constexpr(std::is_same_v<IMS, BasisFactory::FlatLexicographic>)
      return ContainerDescriptors::Impl::flatLexicographicN(children,std::move(subTree));
    else if constexpr(std::is_same_v<IMS, BasisFactory::BlockedLexicographic>)
      return ContainerDescriptors::makeUniformDescriptor(children,std::move(subTree));
    else if constexpr(std::is_same_v<IMS, BasisFactory::BlockedInterleaved>)
      return ContainerDescriptors::Impl::appendToTree(children,std::move(subTree));
    else
      return ContainerDescriptors::Unknown{};
  }
 
protected:
  std::size_t children_;
  SubPreBasis subPreBasis_;
};
 
 
 
namespace BasisFactory {

template<class ChildPreBasisFactory, class IndexMergingStrategy>
auto power(ChildPreBasisFactory&& childPreBasisFactory, std::size_t k, const IndexMergingStrategy&)
{
  return [childPreBasisFactory,k](const auto& gridView) {
    auto childPreBasis = childPreBasisFactory(gridView);
    return DynamicPowerPreBasis<IndexMergingStrategy, decltype(childPreBasis)>(k,std::move(childPreBasis));
  };
}

template<class ChildPreBasisFactory>
[[deprecated("Using the method `power` without an explicit index merging strategy"
  " will change its meaning after the release of dune-functions 2.11."
  " Previously, the default merging strategy was `BlockedInterleaved`,"
  " but this will change to `FlatInterleaved`."
  " Change the call to `power(..., blockedInterleaved())` to retain the old behavior.")]]
auto power(ChildPreBasisFactory&& childPreBasisFactory, std::size_t k)
{
  return [childPreBasisFactory,k](const auto& gridView) {
    auto childPreBasis = childPreBasisFactory(gridView);
    return DynamicPowerPreBasis<BlockedInterleaved, decltype(childPreBasis)>(k,std::move(childPreBasis));
  };
}
 
} // end namespace BasisFactory
 
} // end namespace Functions
} // end namespace Dune
 
 
#endif // DUNE_FUNCTIONS_FUNCTIONSPACEBASES_DYNAMICPOWERBASIS_HH