shared unique_ptr to shared_ptr for old_solution

src/amdis/ProblemInstat.hpp

@@ -54,7 +54,7 @@ namespace AMDiS
     ProblemType const& problemStat() const { return *problemStat_; }
 
     /// Returns const-ref of \ref oldSolution.
-    std::unique_ptr<SystemVector const> oldSolutionVector() const
+    std::shared_ptr<SystemVector const> oldSolutionVector() const
     {
       test_exit_dbg(bool(oldSolution_),
         "OldSolution need to be created. Call initialize with INIT_UH_OLD.");
@@ -81,7 +81,7 @@ namespace AMDiS
     ProblemType* problemStat_;
 
     /// Solution of the last timestep.
-    std::unique_ptr<SystemVector> oldSolution_;
+    std::shared_ptr<SystemVector> oldSolution_;
   };