.Modelica_StateGraph2.UsersGuide.ComparisonWithStateGraph1

Information

The Modelica_StateGraph2 library (called StateGraph2 below) is based on the experience with the current Modelica.StateGraph library (called StateGraph1 below) and is a significantly further development of StateGraph1. Furthermore, it is heavily based on the article (Malmheden et. al. 2008), see literature, but uses a different implementation technique as described in this article. The StateGraph2 library has the following improvements with respect to the StateGraph1 library:

• 3 Basic Components (Step, Transition, Parallel)
  All multiple versions of a component are combined in only one version (e.g., one step and not 4 step components). This is easier to understand and more convenient to use. The "Parallel" component is both used as "composite step" (so only one branch), as well as "parallel step" (so several execution branches).
   
• Conveniently connecting components
  Connecting components of a state machine in Modelica means to provide new vector dimensions and to provide a vector index to connect to. In StateGraph2, the new "connectorSizing" annotation is used and therefore all this is now performed automatically (from a users point of view, these actions are hidden; this is not the case in StateGraph1 and makes the usage of the StateGraph1 library clumsy).
   
• Safer state machines
  It is no longer possible to construct a wrong state machine in the sense that properties of the graph are violated (e.g. two initial steps, or branching wrongly out of a parallel component). Contrary to StateGraph2, in StateGraph1 such wrong graphs do not lead to an error but to unexpected simulation results. Still, other desirable properties of a state machine, such as "no deadlock" or "lifeliness" or "every step reachable", are not (yet) guaranteed with the current StateGraph2.
   
• Composite, autonomous, synchronized, preempted subgraphs
  Composite steps and parallel steps are described in a much better and more powerful way as in StateGraph1: Either by component "Parallel" or by inheriting from "PartialParallel". The first alternative has the advantage that it is simple to use (not necessary to construct a new class and instanciating this class, and easy variable access since no new hierarchy is constructed), the second alternative has the advantage that it introduces a Modelica hierarchy (useful for large subgraphs). In both cases, various options are possible, such as
  1. autonomous subgraphs (branches are executed in parallel autonomously),
  2. synchronized subgraphs (branches are executed in parallel and are synchronized before leaving the subgraph via the outPort),
  3. subgraphs with preemption and exception (a parallel step can be interrupted via the suspend ports and can continue execution via the resume ports).
  This is achieved by enabling/disabling the different ports.
   
• No infinite looping:
  As in StateGraph1, there are two types of transitions: immediate transitions (during event iteration all immediate transitions fire until no transition condition is true anymore) and delayed transitions (a transition fires only after a delay). Contrary to StateGraph1, in StateGraph2 every loop must have at least one delayed transition. If this is not the case a translation error occurs which states that the model contains an algebraic loop between Booleans with the name "checkOneDelayedTransitionPerLoop".
       This property guarantees that an event iteration over a StateGraph2 converges after a finite number of iterations, provided the modeller does not introduce an unsafe construct in the actions associated with a StateGraph2 (e.g. "i = pre(i) + 1" in the equation section outside of a when-clause will give an event iteration that never stops).
       It is possible to switch off this feature, by setting parameter "loopCheck = false" in one transition of a loop, instead of using a "delayed transition" at this place (in cases where immediate transitions are important and the transition conditions are in a form that they cannot fire at the same time instant).