Author: Robert Hyatt
Date: 11:17:15 11/27/00
Go up one level in this thread
On November 27, 2000 at 13:01:04, Scott Gasch wrote:
>Hi all,
>
>I have a standard AB search in my engine right now. It works fine and I am
>reasonably happy with the tree sizes it is searching.
>
>However I am trying to convert it to a PVS -- a search with a minimal window for
>all moves after the first followed, if needed, by a research with the full
>alpha-beta window if this minimal window search returns a score in the original
>a-b range.
>
>As a test I ran the original A-B search from d2d4 d7d5 e2e4 e7e5 to 8 ply and
>compared the number of nodes searched to the new PVS search. I am pretty sure I
>have the PVS implemented correctly and can only assume that the great difference
>in tree size comes from a poor move ordering on my part:
>
> AB PVS
>1. 45 83
>2. 525 646
>3. 3004 4975
>4. 14061 23048
>5. 43460 147922
>6. 183094 633827
>7. 486054 4727636
>8. 1129783 11029952
>
>The strange thing is that I am using the same move ordering in both cases: hash
>move (with PV stuffed), winning captures (MVV/LVA), losing captures (MVV, LVA),
>killers (beta cutoffs at same ply), rest sorted on history heuristic (depth^2).
>
>I've read that some people who use a SEE put losing captures at the end of the
>list. I do not want to do this for two reasons: 1. I generate all captures
>before any of the moves to maybe get a cutoff with less work done and 2. Because
>I do not use a SEE I am not entirely certain that a MVV/LVA capture is indeed
>"losing"... the opponent's piece may be hung and no recapture occur.
>
>Is this move ordering scheme sane?
>
>Thanks,
>Scott
I don't think your losing captures before killers is a good idea. My order:
1. hash move (also includes PV move since it is passed thru hash)
2. winning captures
3. even captures (trades)
4. 2 killer moves (before generating non-captures)
5. 4 history moves (after generating non-captures)
6. rest of moves in order generated, which would put the losing captures
first since I generate captures first.
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