Tutorial Debugging Well-Definedness and Transition Errors: Difference between revisions
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Sometimes you can also have the possibility to click on a "Visualise" button, which in this case will give you a graphical visualisation of the invariant violation: | Sometimes you can also have the possibility to click on a "Visualise" button, which in this case will give you a graphical visualisation of the invariant violation: | ||
[[file:ProB_While_INV_Violation.png| | [[file:ProB_While_INV_Violation.png|200px|center]] | ||
Revision as of 15:33, 25 July 2011
We assume that you have grasped the way that ProB setups up the initial states of a B machine as outlined in Tutorial Setup Phases, and have understood why animation is difficult as outlined in Tutorial Understanding the Complexity of B Animation.
A simple example
Let us use the following B machine as starting point:
MACHINE WhileLoopInvariantError
VARIABLES xx
INVARIANT
xx:NATURAL
INITIALISATION xx:=1
OPERATIONS
Set(c) = PRE c:1..10 & xx<=c THEN
WHILE xx < c DO xx := xx+1
INVARIANT
xx <= c & xx:NATURAL &
xx<10 /* this is wrong */
VARIANT c-xx
END
END;
r <-- Get = BEGIN r:= xx END
END
After loading and initialising the machine you see that ProB has found a so-called "transition error", i.e., an error that occured while computing enabled operations (which correspond to a transition from one state to the B machine to another). These errors are displayed in red in the State Properties pane:
When you click on the red transition error you get presented with more details about the error:
Sometimes you can also have the possibility to click on a "Visualise" button, which in this case will give you a graphical visualisation of the invariant violation:
