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Subject: Re: Computer Correspondence Chess Challenge..... But

Author: Tina Long

Date: 20:17:11 04/01/00

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Hi guys,
This thread has been interesting & generally agreed with previous stuff I'd
read.

So.
Analysing 3 best moves, over 24hours, slows the program by a factor of 3 - 6,
losing 1 or 2 ply depth.

Each extra Ply has a 15% of picking a different move, that the software
calculates is better.

But.
What about the Actual ply depths searched on the 2nd & 3rd preffered moves?
If only the best move is shown, no's 2 & 3 share with no's 4... about 50% of the
search time.

If best three is shown, no's 2 & 3 are receiving 6 - 10 X more thinking time.
1st preferred move has gone from 50% to 25% of thinking time (25% for "rest")
or 1st preferred move has gone from 50% to 17% of thinking time (50% for "rest")

preferences 2 & 3 are being searched an extra 1 - 2 - 3 ply deeper over 24hrs.
Their "score" is more acurate than if only 1 best is shown.

So.
If the "score" of the best 3 moves is not too dissimilar, then "forcing" the
program to look at choices 2 & 3 for longer could be a good thing.

Eg.
guessed ply depths "well" searched for the first four choices over 24 hrs.

Show 1 best:  1-19 2-15 3-15 4-15
Show 3 best:  1-17 2-17 3-17 4-13

Is the "danger" of reducing the favoured move ply from 19 to 17 greater than the
"benefit" of increasing the 2nd & 3rd ply from 15 to 17?

If there is "little to choose" between the best 3 moves, I'd sacrifice the 19 to
17 to pick up the two 15 to 17 searches.  (particularly as I intuitively believe
that the benefit of each extra ply reduces - some say by 0%, I guess by 10%)

Open invitation to shoot my arguments to bits, my appreciation of knowledge on
this exceeds the adamentment of my case.

Sunday,
Clouds but no rain at
Sunny Mount Kembla

Tina Long

On March 31, 2000 at 23:17:45, Robert Hyatt wrote:

>On March 31, 2000 at 12:53:43, Stephen Ham wrote:
>
>>Dear Readers,
>>
>>I know many of you are actively following my ongoing match games versus Fritz 6a
>>and Nimzo 7.32. For those of you not familiar with the event, please visit:
>>
>>http://correspondencechess.com/campbell/index.htm
>>
>>Anyway, a frequent poster here (name is withheld) wrote to Mr. Campbell stating
>>that since the chess engines are displaying their top 3 choices, they are being
>>weakened "a lot". No explanation was given for that claim.
>>
>>Would somebody here please provide a detailed explanation regarding whether this
>>claim is correct and why?
>
>
>It depends on how they compute these variations.  Done correctly, it is
>_horribly_ inefficient.  If you watch a normal search, the first move will
>usually take over 50% of the total time.  The remaining N-1 moves take the
>remaining 50% of the time.  If you have it display two 'best'moves, you
>increase the total search time by roughly 50%.  The first move takes the
>same time as before.  The second move also takes the same time as before,
>and the final N-2 moves take just a tad less than before.  Net loss is
>ugly.  If you have it display the best 3 moves, you slow it down by exactly
>a factor of two...
>
>
>
>
>>
>>The chess engines are on settings recommended by ChessBase USA as their optimal
>>settings for this event. My extremly limited understanding is that displaying
>>the top 3 choices does indeed affect the chess engines, but it causes them to
>>spend more time on what it believes to be the 3 best moves. As such, this sounds
>>like an enhancement to me. Given that the chess engines are allowed about 24
>>hours calculation time on weekdays and are searching to 16-18 ply, I can't
>>imagine that this weakens them in any way.
>
>
>Each iteration will take about 2x longer than the previous.  Rather than
>a branching factor of 3x, you raise it to 6x.  This will cost several plies
>over 24 hours.
>
>
>
>>
>>Please advise. We sincerely want the chess engines to play at peak performance.
>>I also think we all learn more about computers in Correspondence Chess when we
>>can see their 2-3 choices and understand what it caclculates and DOESN'T
>>calculate in certain positions. Often, it seems they make the correct choices
>>for the wrong reasons.
>>
>>Since I am the computer's opponent, I don't have access to the chess engine
>>manuals where this may be explained. Thanks in advance for any information you
>>can provide.
>>
>>Stephen Ham
>
>If the computer is really playing the match, turn N-best _off_ and just play
>the best move it finds...  this is far better...



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