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Subject: Recapture Extensions

Author: Scott Gasch

Date: 13:13:41 06/01/01


Hi all,

I have some questions about recapture extensions.

First of all, what is the point?  I assume to extend in a position where a
recapture move is the only reasonable move so as to see further beyond the
forced exchange.  Somewhat like singular extensions or one legal reply
extensions, I think a properly done recapture extension should not be too
expensive.  I'd also expect that a well done recapture extension would improve
the tactical strength of the engine.

Well, I've been trying to get a good recapture extension working on my engine
for a while now.  I've tried a bunch of different recapture definitions /
conditions.  Most recently I did:

  1. last move was a capture and this move captures the last moved piece
  2. this is the first capture considered (weighed by SEE)
  3. do not allow two recaptures in a row
  4. this move restores the material balance to what it was at the root.

...in which case I extended 1/2 ply.  Since I am expecting better tactical
ability with the recapture turned on, I test it with the ECM suite.  Every time
I try, my results are worse with the recapture turned on than with no recapture.

I know that a bunch of other engines are doing recapture... so there must be a
good idea there somewhere.  Can anyone address these questions or propose a
solid recapture condition?

Thanks,
Scott



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