recipe-iterate-over-grid.cc

See explanation at Iterating over a grid

// SPDX-FileCopyrightText: Copyright © DUNE Project contributors, see file COPYING in module root
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
// C++ includes
#include<math.h>
#include<iostream>
// dune-common includes
#include<dune/common/parallel/mpihelper.hh>
#include<dune/common/parametertreeparser.hh>
#include<dune/common/timer.hh>
// dune-grid includes
#include <dune/grid/yaspgrid.hh>
 
 
int main(int argc, char** argv)
{
  // Maybe initialize Mpi
  [[maybe_unused]] Dune::MPIHelper& helper = Dune::MPIHelper::instance(argc, argv);
 
  // [set up grid]
  const int dim = 4;
  using Grid = Dune::YaspGrid<dim>;
  Dune::FieldVector<double,dim> len; for (auto& l : len) l=1.0;
  std::array<int,dim> cells; for (auto& c : cells) c=4;
  Grid grid(len,cells);
 
  // [extract gridview]
  auto gv = grid.leafGridView();
 
  // [iterate over codim]
  const int codim = 2;
  for (const auto& e : entities(gv,Dune::Codim<codim>{}))
    if (!e.type().isCube()) std::cout << "not a cube" << std::endl;
 
  // [iterate over grid view]
  for ([[maybe_unused]] const auto& e : elements(gv))
    ; // codim=0
  for ([[maybe_unused]] const auto& e : vertices(gv))
    ; // codim=dim
  for ([[maybe_unused]] const auto& e : edges(gv))
    ;    // codim=dim-1
  for ([[maybe_unused]] const auto& e : facets(gv))
    ;   // codim=1
 
  // [access to subentities]
  const int mycodim = 2;
  for (const auto& e : elements(gv))
    for (unsigned int i=0; i<e.subEntities(mycodim); ++i)
      [[maybe_unused]] auto v = e.template subEntity<codim>(i);
}