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Subject: Re: Extensions?!

Author: Don Dailey

Date: 22:35:03 01/14/98

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Hi Bob,

Do you consider fractional plys in your hash table implementation?
Is a depth of 3 3/4 better than 3 1/2?

- Don


On January 14, 1998 at 14:25:41, Robert Hyatt wrote:

>On January 14, 1998 at 08:49:27, Dan Homan wrote:
>
>>On January 13, 1998 at 14:43:16, Robert Hyatt wrote:
>>
>>>On January 13, 1998 at 09:08:49, Dan Homan wrote:
>>>>
>>>>p.s. My program does
>>>>
>>>>capture extensions    (4/10 of a ply)
>>>
>>>dangerous one there.  Ken Thompson used 1/2 ply in 1983, and probably
>>>lost the 1983 World Championship as a result of doing this.  He reported
>>>it helped his WAC results quite a bit, but it costs about 1/2 to 1 ply.
>>>He later discarded it totally.
>>>
>>>
>>>>re-capture extensions (1 ply)
>>>>check extensions      (1 ply)
>>>>pawn push extensions  (1/2 ply or 1/3 ply)  (endgame and late
>>>>middle-game)
>>>>bruce's mate ext.     (1 ply)
>>>
>>>All reasonable.  I am now using 3/4 ply for *everything* in Crafty, but
>>>do allow multiple extensions to add together, with a limit of 1 ply.
>>>This
>>>actually improved the WAC results and seems to be running a good bit
>>>faster
>>>to reach the same depth...
>>
>>You said you allowed multiple extensions to add together with a limit of
>>1 ply.  I assume this means that you do not allow left over fractions to
>>roll over to the next ply.
>
>your wording makes it hard to answer...  but here goes:  At every ply
>along the way, depth gets reduced by 1 ply, as you would expect.  At
>every ply along the way the depth gets incremented by fractional values
>that can not exceed one ply.  So if ply 3 increments by 3/4, and ply
>4 increments by 1, that 3/4 is *not* lost because it came from a
>different ply.
>
>I only restrict a single ply to adding in no more than a one ply
>extension...  but it passes along everything it inherits from prior
>plies.  So a 3/4 extension at ply=1 gets carried along with no real
>effect on the search until someone further along adds in at least 1/4
>more.  Since all of my extensions are currently 3/4, the first 3/4
>doesn't
>do much (this is a lie, more later) but the second 3/4 rolls this up to
>1.5
>plies which extends every line below this by 1 ply.  And the extra 1/2
>is
>kept since it didn't come from the current ply, so that the next 3/4 ply
>will also extend by one, as will the next (but not the 4th).
>
>I said the above is a lie because my initial search depth for a 1 ply
>search is set to 1.75, so that the first 3/4 ply search extension does
>something, as does the 2nd and 3rd.  but the 4th won't, but then we
>start
>over again with the 5th, 6th and 7th extending but the 8th not.
>
>
>
>>
>>I tried eliminating the capture extension, it reduces my search tree
>>by a factor of 2 in most positions so I get about 1 ply deeper in the
>>same time.  I solve some of the WAC positions a ply later, but the
>>speedup generalizes to all positions.  I ran overnight with the new
>>version on FICS, and it doesn't seem any worse (it even gained 20
>>rating points).
>>
>>I'll probably write some analysis tools like Bruce suggested to get
>>a more concrete measure of the change, but I am happy with a smaller
>>search tree. :)
>>
>> - Dan



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