Change type string to StateStructure

include/core/processor/is_motion.h

@@ -34,7 +34,7 @@ class IsMotion
         void addToProblem(ProblemPtr _prb_ptr, IsMotionPtr _motion_ptr);
    
     protected:
-        std::string state_structure_; ///< The structure of the state vector (to retrieve state blocks from frames)
+        StateStructure state_structure_; ///< The structure of the state vector (to retrieve state blocks from frames)
 
 };