brezzidouglasmarini1simplex2dlocalinterpolation.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-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
#ifndef DUNE_LOCALFUNCTIONS_BREZZIDOUGLASMARINI1_SIMPLEX2D_LOCALINTERPOLATION_HH
#define DUNE_LOCALFUNCTIONS_BREZZIDOUGLASMARINI1_SIMPLEX2D_LOCALINTERPOLATION_HH

#include <vector>

#include <dune/geometry/quadraturerules.hh>

namespace Dune
{
  template<class LB>
  class BDM1Simplex2DLocalInterpolation
  {

  public:
    BDM1Simplex2DLocalInterpolation ()
    {
      sign0 = sign1 = sign2 = 1.0;
    }

    BDM1Simplex2DLocalInterpolation (unsigned int s)
    {
      using std::sqrt;
      sign0 = sign1 = sign2 = 1.0;
      if (s & 1)
      {
        sign0 = -1.0;
      }
      if (s & 2)
      {
        sign1 = -1.0;
      }
      if (s & 4)
      {
        sign2 = -1.0;
      }

      n0[0] =  0.0;
      n0[1] = -1.0;
      n1[0] = -1.0;
      n1[1] =  0.0;
      n2[0] =  1.0/sqrt(2.0);
      n2[1] =  1.0/sqrt(2.0);
      c0 =  0.5*n0[0] - 1.0*n0[1];
      c1 = -1.0*n1[0] + 0.5*n1[1];
      c2 =  0.5*n2[0] + 0.5*n2[1];
    }

    template<typename F, typename C>
    void interpolate (const F& f, std::vector<C>& out) const
    {
      // f gives v*outer normal at a point on the edge!
      typedef typename LB::Traits::RangeFieldType Scalar;

      out.resize(6);
      std::fill(out.begin(), out.end(), 0.0);

      const int qOrder = 4;
      const Dune::QuadratureRule<Scalar,1>& rule = Dune::QuadratureRules<Scalar,1>::rule(Dune::GeometryTypes::simplex(1), qOrder);

      for (typename Dune::QuadratureRule<Scalar,1>::const_iterator it=rule.begin(); it!=rule.end(); ++it)
      {
        Scalar qPos = it->position();
        typename LB::Traits::DomainType localPos;

        localPos[0] = qPos;
        localPos[1] = 0.0;
        auto y = f(localPos);
        out[0] += (y[0]*n0[0] + y[1]*n0[1])*it->weight()*sign0/c0;
        out[3] += (y[0]*n0[0] + y[1]*n0[1])*(2.0*qPos - 1.0)*it->weight()/c0;

        localPos[0] = 0.0;
        localPos[1] = qPos;
        y = f(localPos);
        out[1] += (y[0]*n1[0] + y[1]*n1[1])*it->weight()*sign1/c1;
        out[4] += (y[0]*n1[0] + y[1]*n1[1])*(1.0 - 2.0*qPos)*it->weight()/c1;

        localPos[0] = 1.0 - qPos;
        localPos[1] = qPos;
        y = f(localPos);
        out[2] += (y[0]*n2[0] + y[1]*n2[1])*it->weight()*sign2/c2;
        out[5] += (y[0]*n2[0] + y[1]*n2[1])*(2.0*qPos - 1.0)*it->weight()/c2;
      }
    }

  private:
    typename LB::Traits::RangeFieldType sign0,sign1,sign2;
    typename LB::Traits::DomainType n0,n1,n2;
    typename LB::Traits::RangeFieldType c0,c1,c2;
  };
}

#endif // DUNE_LOCALFUNCTIONS_BREZZIDOUGLASMARINI1_SIMPLEX2D_LOCALINTERPOLATION_HH