Author: Joachim Rang
Date: 02:07:26 04/22/03
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On April 21, 2003 at 22:14:17, Rupesh wrote: >Dear All, > >I am puzzled about two parameters in deep fritz 7. The futility pruning and >selectivity. Are not they one and the same thing? > AFAIK futility pruning cuts certain amounts of the searchtree, if further search seems needless (which means, if the evaluation is below a defined margin). Selectivity has probably to do something with reductions and extensions. So certain lines are reduced or extended. The exact implemention of course is unknown. > What impact does it have if i increase the selectivity from default(2) to say 6 >(which is maximum). you will get greater depth and maybe better positional play - but Fritz will miss tactics. What happens if i turn off futility pruning. you will get lesser depth but Fritz may not overlook tactical shots. I have noticed >that deep fritz misses many tactical shots esp in blitz (3 + 2) in complex >positions. If i turn off futility pruning and put selectivity to 0, it picks up >correct moves even in blitz. Surprisingly it does not seem to affect the engine >performance as is often warned ( that with selectivity 0, you will have lots of >junk sort of stuff). For blitz it might be a good idea to turn selectivity down and disable futility pruning. You will reach lesser depth, which will result in weaker positional play and not finding deep tactics. But it might be overcompensated due to the better short-tactical ability. You can be sure, that the default value are very well tested and will give the best overall play (blitz and long time control). It is possible that for blitz some special settings will improve the playing strength. > >Also does changing futility pruning and selectivity have implications for hash >size and contempt value/ draw score. no > >Will be indeed be grateful if somebody can explain the nuances involved here. >Chessbase seems to have an official policy of not disclosing the siginficance of >these parameters. > >Regards and Thanks >Amitesh The exact implementation is secret since this is the creativity of the programmer. So nobody (except the programmer himslef) knows exactly what does selectivity mean. It' a kind of pruning or extensions that is clear.
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