[PL] Vectorized process solutions of previous time step.

ProcessLib/ComponentTransport/ComponentTransportProcess.cpp

@@ -63,6 +63,8 @@ void ComponentTransportProcess::initializeConcreteProcess(
              pv_iter != _process_variables.end();
              ++pv_iter)
             transport_process_variables.push_back((*pv_iter)[0]);
+
+        _xs_previous_timestep.resize(_process_variables.size());
     }
 
     ProcessLib::createLocalAssemblers<LocalAssemblerData>(

ProcessLib/ComponentTransport/ComponentTransportProcess.h

@@ -147,7 +147,7 @@ private:
         _local_assemblers;
 
     /// Solutions of the previous time step
-    std::array<std::unique_ptr<GlobalVector>, 2> _xs_previous_timestep;
+    std::vector<std::unique_ptr<GlobalVector>> _xs_previous_timestep;
 
     std::unique_ptr<ProcessLib::SurfaceFluxData> _surfaceflux;
 };