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Subject: Re: MTD(f) and hash table size

Author: Uri Blass

Date: 11:11:44 08/17/03

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On August 17, 2003 at 13:58:52, Tord Romstad wrote:

>On August 16, 2003 at 17:43:09, Uri Blass wrote:
>
>>On August 16, 2003 at 17:17:26, Tord Romstad wrote:
>>
>>>The last few weeks I have been experimenting with MTD(f).  It still does not
>>>work quite as well
>>>as my old aspiration alpha beta search, but I intend to keep working on it for
>>>some more time.
>>>
>>>One of my biggest worries right now is that the search slows down almost to a
>>>full stop when
>>>the hash table starts getting full.  For instance, here are the time (in
>>>seconds) needed to
>>>finish a 11-ply search from the starting position for different hash table sizes
>>>from 5 to 320 MB:
>>>
>>>5MB: 102 seconds
>>>10MB: 88 seconds
>>>20MB: 78 seconds
>>>40MB: 55 seconds
>>>80MB: 47 seconds
>>>160MB: 34 seconds
>>>320MB: 27 seconds
>>>
>>>Is this normal, or do I have some kind of bug?  I really hope I don't need a
>>>320MB hash table
>>>to play decently at slow time controls.  Should I take a look at my hash table
>>>replacement
>>>scheme?  Currently I always replace if the depth of the new position is >= dept
>>>of old
>>>position.
>>>
>>>Another problem is that MTD(f) has very weird effects when combined with the
>>>various forward
>>>pruning techniques I use.  This is not entirely unexpected, because I use the
>>>values of alpha
>>>and beta for pruning decisions.  When I replace plain MTD(f) (which I haven't
>>>been able to
>>>make work very well; too many researches) with MTD(f) with a convergence
>>>accelerator, I
>>>often get entirely different search results for the same position.  If I remove
>>>all selectivity
>>>(except null move pruning) from my search, changing the test driver does not
>>>have any
>>>effect on the search results, but then my program becomes much too slow.  I
>>>suppose I
>>>will have to work out new forward pruning techniques.
>>>
>>>Tord
>>
>>Why?
>>Maybe your forward pruning is superior to MTD.
>>
>>The fact that MTD is not good for you because of your forward pruning does not
>>mean that your forward pruning is bad.
>
>I don't really like my forward pruning.  I am beginning to become sceptical to
>all
>pruning schemes which involve the values of alpha or beta.  Even in plain
>aspiration
>search there are problems when such pruning is combined with hash tables.

I guess that not for me because I do not use the hash tables for pruning.

I also use alpha or beta for my pruning decisions and I plan to add in the
future more rules that are going to use alpha and beta.

Uri



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