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Subject: Re: Testing the reliability of forward pruning

Author: Robert Hyatt

Date: 07:42:25 05/16/03

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On May 15, 2003 at 21:47:20, Jon Dart wrote:

>Ernst Heinz did this by using standard test suites, for example Win at Chess, or
>ECM (Encyclopedia of Chess Middlegames). He found that the solve rate didn't
>really change much with forward pruning on, but the number of nodes searched for
>a fixed ply depth decreased 20-50% (this is from the chapter on AEL pruning in
>his book Scaleable Search in Computer Chess). He also used other testing
>methods, including game play, as detailed in the book.


I don't think this methodology is reasonable.

For example, suppose your forward-pruning speeds you up by a factor of
four.  Comparing same-search-depth runs means the FP version will move
in 1/4th the time of the non-FP version.  Suppose the FP version does
worse on three positions?  But if you run it for 4x longer, so that it
has the same time limit as the non-FP version, the three positions are now
"back to normal"???

I think the _right_ way to test is with a fixed time limit so that a version
that can go deeper will go deeper.  After all, that is the _purpose_ of FP
in the first place...




>
>--Jon
>
>On May 15, 2003 at 18:17:09, Russell Reagan wrote:
>
>>I would like to know how to test whether or not a forward pruning method is
>>reliable.
>>
>>I have one idea to test when and if a method is reliable, and I'd like to know
>>if it's a good idea or not, and also what other methods might be used to test
>>the reliability of forward pruning methods.
>>
>>My idea requires a collection of games, and two versions of a program. One
>>version would have forward pruning turned off, and the other would have it
>>turned on. You would feed each version of the program the same game, and let
>>each do a search on the initial position to the same fixed depth. If both
>>versions report the same move and score, and the version using forward pruning
>>had a lower time to depth, then the forward pruning is reliable (so far). If the
>>version using forward pruning reported different results, then the forward
>>pruning method is not reliable for this type of position. You make the next move
>>in the game, and repeat the search and compare the results for each position in
>>the game. Then you repeat the process for each game.
>>
>>When I think about testing the reliability of null-move using this method, I
>>think the test would do well. I would expect the test to tell us that in most
>>positions, null-move is reliable, and I would expect it to fail for some endgame
>>positions, and so this test would tell us that null-move was good forward
>>pruning, but to turn it off in the endgame (or detect zugzwang, or however you
>>choose to guard against it). I haven't had time to test this though, since I
>>just thought of it and I'm not at home.
>>
>>I am basing all of this on the assumption that the strength forward pruning
>>provides is not that it finds better moves at the same depth, but that it
>>finishes searching a particular depth in a shorter amount of time, allowing the
>>search to go deeper, which is where the added strength comes from. Is this
>>correct?
>>
>>Comments, please...



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