recipe-integrating-grid-functions.cc

See explanation at Integrating grid functions

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
 
#include <iostream>
 
#include <dune/common/filledarray.hh>
#include <dune/common/parallel/mpihelper.hh>
 
#include <dune/grid/yaspgrid.hh>
 
#include <dune/pdelab.hh>
 
int main(int argc, char** argv)
{
  // Initialize Mpi
  Dune::MPIHelper::instance(argc, argv);
 
  // need a grid in order to test grid functions
  constexpr unsigned int dim = 2;
  Dune::FieldVector<double,dim> L(1.0);
  std::array<int,dim> N(Dune::filledArray<dim,int>(64));
 
  typedef Dune::YaspGrid<dim> Grid;
  Grid grid(L,N);
 
    // [Defining an analytic grid function]
    auto analyticFunction = Dune::PDELab::makeGridFunctionFromCallable (grid.leafGridView(), [&](const auto& x){
      return exp(-(x*x));
    });
 
  // [Compute integral]
  auto integral = Dune::PDELab::integrateGridFunction(analyticFunction,10);
 
  // [Sum for parallel case]
  integral = grid.leafGridView().comm().sum(integral);
 
  std::cout << "Integral: " << integral << std::endl;
}