Rationale

For a discrete event dynamic system it is common that when an individual action occurs that it assigns new values only to a small subset of state variables. So most state variables retain their old values and the state transformation that those variables experience is an identity function. This is normal and expected behavior. The fact that an action does not change the value of a variable is represented in a trace by not making any assignments to that variable.
For efficiency reasons, a DEDS simulation should focus on state changes that truly change state.

Symptoms

The warning is raised because there is at least one event in the trace that is attributed to action A where A explicitly assigns a value to state variable V and this new value happens to be the same as before.
Note that this does not(!) mean that the full state descriptions are the same. The warning only refers to the value of a single particular variable V and usually the state of a simulation models is described by a multitude of variables.

Diagnosis

• The specification of action A contains a useless, redundant assigment statement for variable V. This implies that the redundant assignment is likely to be observed whenever A occurs.
• The simulator internally performs useless value assignments.
• The simulator does not perform those value assignments but reports a full state descriptor for every state in the trace. This implies similar warnings for all state variables.
• The value assignment is due to specific behavior of action A, e.g., A performs a reset operation that sets certain state variables back to a specific value and independently of any previous state. This behavior includes a reassignment of the same value as a special case. This implies that the redundent assignment is likely to occur only for specific situations and not all the times when A occurs.

Verification and Therapy

• Check the model specification for action A. If it contains a useless assignment to variable V, reconsider what A is supposed to do and if the value of V needs not be changed, then remove the assignment to avoid unnecessary work performed by the simulator. Rerun the simulation to check if the warning has disappeared.
• Check if all pairs of actions and variables generate this warning, which makes it likely that the simulator either internally performs useless operations or generates full state descriptions in the trace generation. If you have access to the simulator code, see if you can get rid of the redundant operations.
• Check occurrence of A in the trace with Traviando's trace visualization, in particular with the event browser. Check individual locations where A occurs to see if the reassignment of values to V happens consistently throughout the trace which indicates that there is a problem with the specification of A or only occassionally which indicates that A may have this property and which may be acceptable as it is. Traviando helps you to identify the particular states where A happens with its event browser.