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Subject: Re: History Heuristic on its own

Author: Will Singleton

Date: 19:38:30 01/19/99

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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.
>

Chris,

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.

Will



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