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Subject: Re: nullmove and tactics

Author: Roberto Nerici

Date: 00:42:00 03/26/04

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On March 26, 2004 at 03:02:04, Tord Romstad wrote:

>On March 26, 2004 at 02:39:29, Johan de Koning wrote:
>
>No, I do lots of pruning besides null-move, and reach rather high search
>depths even without it.  Here are the number of nodes I need to search
>n plies (n from 1 to 13) with and without null move from the opening
>position:

I think this makes a big difference to the result of the null move versus
non-null move test. Most people when first writing an engine (this includes me)
add null-move to a search that has no other pruning at the time and this makes a
huge difference.

People here have pointed out several times that pruning schemes overlap; any one
scheme is usually more effective on its own that in combination with others.

>Plies   Nodes (null move off)   Nodes (null move on)
> 1                 55                      55
> 2                228                     261
> 3                965                     439
> 4              3,741                   2,318
> 5             13,213                   6,638
> 6             35,056                  18,964
> 7             37,398                  36,095
> 8             77,226                  60,240
> 9            117,274                 109,939
>10            239,355                 237,775
>11            555,661                 412,969
>12          1,942,523               1,084,089
>13         12,060,312               3,531,279
>
>I have no good explanation for the bizarrely irregular effective
>branching factor of my non-nullmove search here.  I wonder how it is
>possible that hardly any nodes are needed in the 7th iteration.

Two possibilities:
1) there's something wrong at the 7th iteration
2) you've stumbled onto something amazing at your 7th iteration and just need to
make it do the same thing on the later ones... :->

Roberto/.



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