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