question about hash in todays competition play

[kgburcham]

do some programs clear hash with every move or maybe with every two ply?

kgburcham

[Gian-Carlo Pascutto]

Mine never ever clears hash.

[bob]

Mine never ever clears hash.

I never clear the hash. I do, on rare occasions run thru and flag all scores as invalid, such as when I near the 50-move rule so that hashed scores/bounds won't hide 50-move draws. The entries stay with the best moves however.

[M ANSARI]

Although I can see some immature engine as clearing hash due to bug avoidance, I think that would be counterprocutive for a mature engine and well worth the effort in making the code clean enough to avoid bugs. Hash should in effect improve an engine's play as it has plenty of information that it gathered during pondering which it does not have to calculate again. Rybka 3 had some interesting ideas where it uses this information in a format which could be transferred or saved for later use, thus greatly aiding in analysis. This was somehow buggy though and hopefully R4 will have that fixed. I find that to be extremely useful in book or opening analysis as without it you are basically starting from scratch everytime you startup a certain position.