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Subject: Re: History Heuristic on its own

Author: Will Singleton

Date: 08:47:38 01/20/99

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On January 20, 1999 at 10:17:40, Robert Hyatt wrote:

>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)...


Yes, I'm sure I have some ordering issues to work out.  It's actually a miracle
it works at all.  And the above numbers were from a small sample.

I use killers a little differently than others.  I try them after good caps, and
maintain a list of 4 best.  So it's rather more like a mini-HH than killers.


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