[Extern] Register with MPI

This is now necessary even though the code is entirely serial.

src/one-body-problem.cc

@@ -17,6 +17,7 @@
 #include <dune/common/fmatrix.hh>
 #include <dune/common/function.hh>
 #include <dune/common/fvector.hh>
+#include <dune/common/parallel/mpihelper.hh>
 #include <dune/common/parametertree.hh>
 #include <dune/common/parametertreeparser.hh>
 
@@ -72,6 +73,7 @@ Dune::ParameterTree getParameters(int argc, char *argv[]) {
 
 int main(int argc, char *argv[]) {
   try {
+    Dune::MPIHelper::instance(argc, argv);
     auto const parset = getParameters(argc, argv);
 
     MyGeometry::render();