Nov 6, 2011

[Info] Fun little problem

Still tuning, moved on to passed pawn eval which is another of those problem areas (I've always thought Mediocre neglected passed pawns, but any attempts to manually tune it has resulted in heavily overvaluing them).

While running my tests I ran into a little interesting problem. Since I have aspiration windows it's quite common that researches occur (when the result is outside the window, i.e. a sudden drop/rise in evaluation between iterations).

Now if not careful it's possible that this window bounces back and forth, i.e. failing too low, then too high and never getting passed the iteration since it keeps researching.

I have all those security measures in place, but with the extreme numbers in evaluation the tuning can come up with, the score was so high it surpassed the "infinity" score. Now this will obviously fix itself after a few iterations of the testing (giving a passed pawn the value of 20 queens is probably not going to help), but my aspiration windows went berserk since I check it like this:

if(eval <= alpha) {
} else if (eval >= beta) {

With alpha and beta set to - and + "infinity" we have the maximum window that can never cause a research (mate in 1 is lower than infinity obviously). But as I said with these extreme evaluation parameters it did.

Easy fix, just a bit silly and quite hard to find.

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