Call LoopSolver::preprocess()

src/one-body-sample.org

@@ -405,6 +405,7 @@
         (multigridStep, parset.get<size_t>("solver.tnnmg.maxiterations"),
          parset.get<double>("solver.tolerance"), &energyNorm, verbosity,
          false); // absolute error
+        overallSolver.preprocess();
         overallSolver.solve();
       };