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Subject: Re: History Heuristic on its own

Author: Robert Hyatt

Date: 21:04:52 01/16/99

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On January 16, 1999 at 21:22:28, Chris Moreton wrote:

>I am in the process of conduction a number of tests regarding the performance of
>alpha-beta and its various enhancements using Rival.  Clearly a wealth of
>information and publications exist already on this subject and it may be
>considered no longer interesting but my reasons are also to see how much effect
>other search parameters have on the engine, notably, the quiescense search and
>search extensions.  The tests searching the 10 nunn positions to depths 2 thru 7
>for various combinations of AB enhancements.
>The question I would like to ask regards the history heuristic.  Jonathon
>Schaeffer's work on the HH (The HH and AB search enhancments in practice) shows
>that it provides significant gains when applied to plain AB with no knowledge
>move ordering and slightly more gains when used in conjunction with knowledge
>ordering.  JS mentions that in his test program that there was a certain amount
>of move ordering even when no knowledge was applied (e.g. capture moves were
>generated first).
>My results indicate that when the move order is fully randomised, the HH has no
>positive effect on node count when added to plain AB, often exceeding the pure
>AB figure.  Other results from my tests regarding the HH seem consistent with
>JS's observations and show that at least up until depth 7, HH outperforms a
>transposition table with approx. 300,000 entries when applied to AB+Knowledge
>ordering + Minimal Window searching.
>Am I implementing the HH incorrectly, or are these results consistent with
>others observations?

The history heuristic is 'global' in nature, in that moves from all over the
tree affect the history counts and hence move ordering.  This should _never_
be better than the hash table move or non-losing captures.  _ever_.  If it is,
something is wrong somewhere else, because the hash move is specific and not
global.  IE this move was best in _this_ position before...

Random move ordering isn't interesting to test, because you get random

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