Fix computation (Don't ask me why this is a fix!)

src/myblockproblem.hh

@@ -125,8 +125,8 @@ class MyBlockProblem<ConvexProblemTypeTEMPLATE>::IterateObject {
         Dune::minimise(localJ, ui_copy, correction);
         ui_copy += correction;
       }
-
-      ui = ui_copy;
+      // FIXME: this makes no sense. Why does it work this way?!
+      ui -= ui_copy;
       return;
     }