message: Add comment poisson-sover
diff: @@ -164,7 +164,8 @@ int main(int argc, char* argv[])
  // executor used by the application
  const auto app_exec = exec->get_master();
  - // problem:
  + // Set up the problem: define the exact solution, the right hand side and
  + // the Dirichlet boundary condition.
  auto correct_u = [](ValueType x) { return x * x * x; };
  auto f = [](ValueType x) { return ValueType(6) * x; };
  auto u0 = correct_u(0);
  