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Subject: Re: History Heuristic on its own

Author: Robert Hyatt

Date: 07:17:40 01/20/99

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On January 19, 1999 at 22:38:30, Will Singleton wrote:

>On January 16, 1999 at 23:19:04, Chris Moreton wrote:
>>Cutoffs in the full width triggers a history entry which adds a value which is 2
>>to power Depth to the from-to array.  When a history entry reaches a certain
>>value, all the values are halved.
>Here's the results for my program on your HH question.  Sorry it took so long,
>but I had to get a block of time to do it.
>Amateur 0.9g
>PVS Search - 7 ply
>Results are average nodes from a small test suite.
>No enhancements                  23,000,000
>HH only                           9,000,000
>TT only                           6,700,000
>HH + TT                           3,000,000
>HH + TT + killers                 2,150,000
>HH + TT + killers + caps          1,860,000
>HH + TT + killers + caps + null     635,000
>all except HH                     1,100,000
>all except TT                     1,700,000
>So it appears that the HH is significant both by itself, and in combination with
>the others.  This is PVS as opposed to plain AB, but I don't think that should
>make a lot of difference.
>The fact that you don't get a reduction when using HH by itself is troublesome.
>I would guess that you might have a bug somewhere.  Try looking at the move list
>in the debugger for various positions, seeing if it looks reasonable.  You also
>might try not storing HH values when depth <= 2.  And using depth * 2 might be
>faster than 2 to the depth.
>Good luck.

Just a note that using _all_ of those should not continuously drop your
node count.  Remember that at some nodes we search _all_ moves and ordering
is worthless there.  And at other nodes we want to fail high after 1 move.

I added killers, not because they made the tree smaller (since they are just
a special case of history) but because I can try those two non-capture moves
before generating any non-capture moves (which saves time, not nodes).

I would suspect that you may still have some move ordering issues to clean up
based on your numbers, because I can take out either history or killer and
my node count doesn't shoot way up (unless I remove both)...

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