Integrating grid functions

First, we define some example grid function to integrate.

    auto analyticFunction = Dune::PDELab::makeGridFunctionFromCallable (grid.leafGridView(), [&](const auto& x){
      return exp(-(x*x));
    });

Computing the integral of a grid function is just a single call:

  auto integral = Dune::PDELab::integrateGridFunction(analyticFunction,10);

When run in parallel, this integrates over the local interior domain. So, in that case, we still need to sum over all processes for the full integral.

  integral = grid.leafGridView().comm().sum(integral);

Full example code: recipe-integrating-grid-functions.cc