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Subject: History Heuristic on its own

Author: Chris Moreton

Date: 18:22:28 01/16/99


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?

Chris



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