Apr 2, 2007

[Other] Struggling with futility pruning

About two months ago I tried implementing futility pruning. I failed miserably and decided to blame it on the general structure of Mediocre at the time. :)

Once again I am trying to get it to work and obviously I am doing something terribly wrong. I have tried three different setups and run 100 games matches against version 0.3, all three setups resulted in weaker play.

The theory is so simple that I must be missing something.

Well I will keep trying this time.

1 comment:

Teemu Pudas said...

A few possible reasons why it might be failing for you:

1)If your depth 1 margin is too high, the opponent will just stand pat in a lot of positions you could have pruned safely. For example, Toga uses 100 (about 1.25 pawns).

2)It's not worth trying in PV nodes (since the eval is most likely going to be too high and there are so few of them anyway).

3)Can Mediocre sort a non-check non-capture in front of a check? If yes, calling a checkless qsearch without ever searching that check will make you miss many mates.

Also, as H.G. Müller pointed out in the Winboard forum a while back, razoring seems useless. It simply makes the move even more futile, and it'd therefore be better to prune it altogether.