Author: Robert Hyatt
Date: 05:11:04 02/16/99
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On February 16, 1999 at 04:45:43, Frank Schneider wrote: >I experimented a little bit with nullmove deepsearch extensions and with >singular extensions and now I have some questions: > >1. In all my tests the searchtree (#nodes to finish n iterations) increased > by a factor of 1.5 to 4. Although testresults were interesting I believe > this is too much. What are your experiences? when I added singular extensions to Cray Blitz, the 'cost' was one ply. which was about a factor of 5 in speed or nodes. > >2. Is it correct to assume that singular extensions work best if there are > only few other extension heuristics. not at all, but you have to be careful as it is possible to over-extend and drive the tree wild... Getting out of check is not singular 99% of the time, so discarding that would cause tactical trouble.... others would probably hurt also. IE in CB I didn't take anything out... but you do avoid the singular test in some cases (in check with only one legal move is obviously singular, but I already extend for one-reply so the singular test doesn't happen.) > >3. How would you describe the difference between nullmove deepsearch extensions > (Donninger) and the nullmove threat detection by Deep Thought? The ideas are similar, based on the result the null-move search returns. I found this not particularly good around version 8-9 in Crafty. I tried both singular and null-move threat extensions, and didn't like them back then. But hardware has come a long way, so that giving up a ply now would not kill my performance. Singular extensions (at least a fairly easy to implement version) is being tested right now by one crafty clone on ICC. > >4. Who uses > - singular extensions > - nullmove deepsearch extensions > - nullmove threat detection > >5. What is the best (easiest) way to implement singular extensions? > if you mean 'real singular extensions' there is only one way to do this, as explained in the deep thought extension article. It is non-trivial to do right, otherwise you have to sort thru a lot of search inconsistencies causes by a move extending at ply=n, but not at ply=n+1, etc.. I don't know of anyone using real singular extensions other than Deep Blue and Cray Blitz (this being both PV-singular and FH-singular extensions). > >Thanks in advance, > >Frank
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