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Subject: Re: MTD concept and why PVS is superior

Author: Bo Persson

Date: 14:15:13 06/22/05

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On June 22, 2005 at 10:01:12, Vincent Diepeveen wrote:

>On June 21, 2005 at 16:11:50, Bo Persson wrote:
>
>>On June 20, 2005 at 08:06:08, Vincent Diepeveen wrote:
>>
>>>
>>>If at 13 ply the score of other moves is 0.35 or so and from this root move it's
>>>0.400, then we have a 100 point difference between 0.300 and 0.400.
>>>
>>>Now we need possibly a 100 researches to get to 0.400, but at least 2 dozen or
>>>so. As we will use bounds 0.300 0.301 0.302 0.303 0.304, hoping that the score
>>>is close to 0.300 of iteration 12 of course.
>>>
>>>PVS is far superior in this as we can determine the true bound directly by
>>>taking the tree of 12 ply search depth. We add 1 ply to it and we already have a
>>>root score of real close to 0.400 to it. So for the price of a node or 50 using
>>>hashtables we directly determine a true bound or somethign real close to the
>>>true bound, where MTD needs 20+ researches for.
>>>
>>>Is my point clear now?
>>
>>This is the usual Vincent thing - he can't get it to work, so it just doesn't
>>work.
>>
>>Who said you had to add 1 millipawn for each research? You can accellerate the
>>step (+16, +32, +64, etc), until you step over the target, and then zoom in
>>again.
>>
>>To go from 0.300 to 0.400, my program tries this series:
>>
>>0.300 0.316 0.348 0.412 (fail low!) 0.380 0.396 0.404 0.400
>>
>>That's eight (8) searches, not 100, not even 20+ !
>
>>Bo Persson
>
>By not using step 1 initially you remove all advantages that MTD *might* offer.

No.

If the final score would actually be 0.301, I would go

0.300 0.316 0.308 0.304 0.302 0.301

That's 6 null window searches. Not bad.

Of course, if the new score just happened to be 0.316, I would find it really
fast!

Why optimize for the 0.300 -> 0.301 case? Is that very frequent in your program?


Bo Persson



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