While looking over the SimpleEvaluator code, I noticed that the package-private field "Population oldpop = null;", which is used as a swap variable, never has a value assigned to it. As such, any call to "contract()" will set state.population to null. This could be a bug affecting the behavior of the "num-test" parameter, described in section 6.1.6 of the manual.
The line "Population oldpop = state.population;" appears at the end of "expand()" and does nothing. This should probably be changed to read "this.oldpop = state.population".
I'm not currently using this feature, and I haven't played with this to verify the bug or the fix.
Ph.D student in Computer Science
George Mason University