LocalDOF.h

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#pragma once
 
#include <boost/mp11.hpp>
 
#include "NumLib/Fem/ShapeMatrixPolicy.h"
 
namespace NumLib
{
template <typename ShapeFunction, int Dim>
struct Vectorial
{
};
 
namespace detail
{
template <typename ShapeFunction>
struct NumberOfDofs : std::integral_constant<unsigned, ShapeFunction::NPOINTS>
{
};
 
template <typename ShapeFunction, int Dim>
struct NumberOfDofs<Vectorial<ShapeFunction, Dim>>
    : std::integral_constant<unsigned, ShapeFunction::NPOINTS * Dim>
{
};
 
template <typename... Ns_t,
          typename ElementDOFVector,
          int... Offsets,
          int... Sizes>
auto localDOFImpl(ElementDOFVector const& x,
                  boost::mp11::mp_list_c<int, Offsets...>,
                  boost::mp11::mp_list_c<int, Sizes...>)
{
    static_assert(((Sizes > 0) && ...));
    static_assert(((Offsets >= 0) && ...));
 
    return std::tuple<Eigen::Map<typename MatrixPolicyType::VectorType<
        NumberOfDofs<Ns_t>::value> const>...>{{x.data() + Offsets, Sizes}...};
}
}  // namespace detail
 
template <typename... Ns_t, typename ElementDOFVector>
auto localDOF(ElementDOFVector const& x)
{
    using namespace boost::mp11;
 
    static_assert(sizeof...(Ns_t) > 0);
 
    using Sizes = mp_list_c<int, detail::NumberOfDofs<Ns_t>::value...>;
    using Offsets =
        mp_push_front<mp_pop_back<mp_partial_sum<Sizes, mp_int<0>, mp_plus>>,
                      mp_int<0>>;
 
    assert((mp_back<Offsets>::value + mp_back<Sizes>::value == x.size()) &&
           "The passed shape matrices require a different number of "
           "d.o.f.s than present in the passed element d.o.f. vector.");
 
    return detail::localDOFImpl<Ns_t...>(x, Offsets{}, Sizes{});
}
 
}  // namespace NumLib