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Subject: Re: When to do a null move search - an experiment

Author: Vincent Diepeveen

Date: 18:05:11 04/27/04

Go up one level in this thread


On April 27, 2004 at 17:10:16, Dann Corbit wrote:

>On April 27, 2004 at 06:10:04, Vasik Rajlich wrote:
>
>>On April 27, 2004 at 01:38:49, Uri Blass wrote:
>>
>>>On April 27, 2004 at 00:44:34, rasjid chan wrote:
>>>
>>>>On April 26, 2004 at 20:07:00, Uri Blass wrote:
>>>>
>>>>>On April 26, 2004 at 13:41:53, Vincent Diepeveen wrote:
>>>>>
>>>>>>On April 26, 2004 at 12:14:33, José Carlos wrote:
>>>>>>
>>>>>>>On April 26, 2004 at 11:57:43, Vincent Diepeveen wrote:
>>>>>>>
>>>>>>>>On April 26, 2004 at 11:48:35, José Carlos wrote:
>>>>>>>>
>>>>>>>>>On April 26, 2004 at 11:32:26, Tord Romstad wrote:
>>>>>>>>>
>>>>>>>>>>On April 26, 2004 at 10:39:42, José Carlos wrote:
>>>>>>>>>>
>>>>>>>>>>>  An interesting experiment, of course. But I think your conditions are rather
>>>>>>>>>>>different from 'most' programs. I mean:
>>>>>>>>>>>  - You allow any number of null moves in a row (most programs don't do even
>>>>>>>>>>>two)
>>>>>>>>>>
>>>>>>>>>>This has no importance, I think.  My experience is that I almost always get the
>>>>>>>>>>same score and PV when I enable/disable several null moves in a row, and that
>>>>>>>>>>the difference in number of moves searched is *very* tiny.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>  You're probably right, as you've tested and I speak from intuition, but at
>>>>>>>>>first sight, it seems that the fact that you allow several null moves in a row
>>>>>>>>>will increase your percentage of null-moves-tries/total-nodes-searched, and thus
>>>>>>>>>that avoiding unnecessary null moves will be a good idea.
>>>>>>>>
>>>>>>>>In *all* experiments i did with nullmove and a program not using *any* forward
>>>>>>>>pruning other than nullmove, the best thing was to *always* nullmove.
>>>>>>>
>>>>>>>
>>>>>>>  Yes, that's what other programmers also said (including me) in the thread we
>>>>>>>had last week. That's pretty intuitive. With not any other forward pruning (or
>>>>>>>very little) but null move, the cost of not trying a null move that would have
>>>>>>>produced a cutoff it terrible compared to the benefit of saving an useless null
>>>>>>>move try. So avoid null move, in this case, must be only in a very few cases
>>>>>>>where you're 99.99% certain you'll fail low... if any.
>>>>>>
>>>>>>99.99% means 1 in 10k nodes.
>>>>>
>>>>>No
>>>>>
>>>>>You can be 99.99% sure about fail low more often than 1 in 10k nodes.
>>>>>
>>>>>>
>>>>>>So doing nullmove always is cheaper, because in a lot of cases
>>>>>>transpositiontable is doing its good job and in other cases you search more than
>>>>>>10k nodes which you avoid searching now.
>>>>>>
>>>>>>>  Gothmog is very different from that 'paradigm' (he does a lot of forward
>>>>>>>prunning and applies many ideas he has commented here), hence it works pretty
>>>>>>>well for him.
>>>>>>
>>>>>>I get impression evaluation function plays a major role in when something is
>>>>>>useful or when it isn't.
>>>>>>
>>>>>>Checks in qsearch is also a typical example of this.
>>>>>>
>>>>>>>
>>>>>>>>Double nullmove i invented to proof nullmove gives the same results like a
>>>>>>>>normal fullwidth search for depth n which i may pick, and i use it as it finds
>>>>>>>>zugzwangs and i am sure that is very helpful, because the weakest chain counts.
>>>>>>>>
>>>>>>>>So double nullmove always completely outgunned doing a single nullmove then
>>>>>>>>disallowing a nullmove and then allowing the next one.
>>>>>>>
>>>>>>>  I tried double null move some time ago, and it didn't work for me. Probably I
>>>>>>>did something wrong, but I recall an old post (see the archives) from C. Theron
>>>>>>>where he gave some points why double null move should not work. I, myself,
>>>>>>>didn't invest too much time though as I had much weaker points to fix in my
>>>>>>>program before.
>>>>>>
>>>>>>Christophe didn't post it doesn't work AFAIK.
>>>>>>
>>>>>>Further i must remind you that majority of commercial programmers posting here
>>>>>>is not busy letting you know what works for them or doesn't work for them.
>>>>>>
>>>>>>To quote Johan: "don't inform the amateurs".
>>>>>
>>>>>What reason do you have to tell other what works for you and what does not work
>>>>>for you?
>>>>>
>>>>>You do not plan to inform the amateurs about better code for tablebases than the
>>>>>nalimov tablebases so I do not see you as a person who try to help the amateurs.
>>>>>
>>>>>>
>>>>>>I remember that Christophe also posted that evaluation function is not so
>>>>>>important.
>>>>>>
>>>>>>His latest postings here made more sense however than the crap posted before
>>>>>>that.
>>>>>
>>>>
>>>>>I understand that you claim that basically Christophe's claim that most of the
>>>>>improvement in tiger came from better search and not from better evaluation was
>>>>>disinformation.
>>>>
>>>>Firstly there is not that BIG a stake for disinformation and posting
>>>>here is also just normal human behaviour that does not require
>>>>asking "....why do I post ? ". Then also ask why do I talk.
>>>>
>>>>I think Christophe was quite clear about the reasons why chess programming
>>>>is NOT about evaluation(not dumb evaluation). After pawn structures, passed
>>>>pawns etc, it is very difficult to try to improve on it. The curve for
>>>>evaluation is logarithmic for elo-increase/code-increase + huge overhead,
>>>>the very reverse of exponential.Search almost have no trend patterns and
>>>>search improvements usually have no overhead, you just need to be smarter
>>>>then the rest. Assume your opponent searches on average 3 plys ahead.
>>>>How do you do a good evaluation that can see 3 plys ahead? Evaluation is horizon
>>>>dumb.
>>>>
>>>>Rasjid
>>>
>>>I did not claim that christophe claimed wrong things.
>>>It is Vincent who claimed it.
>>>
>>>I prefer not to talk about the top programs.
>>>I can only say that it is clear for me that I can get much by search
>>>improvements.
>>>
>>>Certainly searching 3 plies forward or doing something equivalent can help
>>>significantly but the problem is how to do it.
>>>If you are optimistic about doing it with no price by intelligent extensions and
>>>reductions
>>>and better order of moves then it is clear that going for search is the right
>>>direction.
>>>
>>>If you are not optimistic even about getting something equivalent to 1 ply
>>>forward then evaluation is the right direction.
>>>
>>>Uri
>>
>>I don't think you need objective answers to these questions.
>>
>>You just need a game plan.
>>
>>A plain, reasonably tuned eval combined with a state of the art selective search
>>seems like a perfectly reasonable game plan to me.
>>
>>Ditto for plain search combined with a state-of-the art evaluation.
>
>Bruce Moreland (who's program Ferret was at one time among the top two or three
>in the world) found a great annoyance when as he improved his evaluation: he
>discovered that he was then being outsearched.
>
>I think the lesson is simple:
>If your new smarter eval makes the program stronger, then keep the new
>evaluation terms.  If not, rip them out.

I feel search is overrated too much. It's so so hard to make a good eval, only
when you have a real well tested and tuned eval making a good search is
important.

Even searching fullwidth i can beat Crafty.

In fact i saw diep at a P4 2.8Ghz in blitz beat crafty at its dual Xeon lately
at icc. I was pretty amazed because i always say that you need at least 12-14
ply to search outside tactical barrier.

Perhaps i'll change that back to 10 ply one day :)






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