Author: Dieter Buerssner
Date: 08:48:36 11/12/05
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On November 12, 2005 at 09:20:07, Albert Silver wrote: >Over at CSS, the latest results of CEGT were shown with both Fruit 2.2 and Fruit >2.2.1 having achieved the exact same rating. The poster concluded this reflected >the myth that TBs added strength, whereas the ratings proved otherwise. I view >it differently of course. What *can* be concluded is that the speed lost >searching the TBs on the HD is compensated by the knowledge brought. I think, this cannot be concluded. Robert Allgeuer has reported some interesting tests some time ago, where the results are similar. However, he did not see much slow down due to TBs in game phases, where the game was not already decided. I believe, things are more complicated here. I suspect, that TB accesses change the search tree in some unfavorable way. Some random observations from selected positions (out of my memory): - I have seen positions, where the result was a win for one side - with TBs the engine showed draw score for larger depths, while without TBs the score continually increased - I had tried "fail hard" TB scores vs. "fail soft" TB scores. Fail hard means: return beta or alpha in case where the TB score is out of the search window. Fail soft means: return result from the TB. To my surprise, fail hard often was faster. Hard to explain. Of course, there are many positions, where the slow down due to the TB-accesses makes the engine slower to find the best move. But because of Robert Allgeuers results, I don't believe this is the main reason to explain the results, that have been reported. The testing environment of the results of Helmut Conrady in CSS some time ago was also not described in all detail. For example, it is not known (to me - I had asked at the time) in which order the tests had been done, whether learning was cleared between the tests, and I seem to remember vaguely some more issues. It is clear, that TBs should always help for not too short time control. Only using them at the root can never hurt (just recently Yace lost a game vs. Crafty in KRPPKR, which was a TB draw, Crafty used this TB, Yace didn't). One can tune the engine in a way, that there is practically no slow down, by only accessing TBs very close to the root position. BTW. There are also many (?) (study like) position, where one can find, that using TBs extremely aggressively (during the whole search) will help to find the solution much faster. Even when nodes/s goes down to perhaps 5% of the usual value. Regards, Dieter
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