Author: Sune Fischer
Date: 06:51:16 04/06/03
Go up one level in this thread
On April 06, 2003 at 07:40:11, Ian Kennedy wrote:
>Has anyone done this in their program? I have been trying recently. One of the
>problems is that the standard formula for the size of a minimal tree assume a
>fixed branching factor. I've manually worked out what the figures are for a
>branching factor bf[depth] for the first few plies but gave up after that. I've
>just read a paper by Schaeffer in which he refers to a technique suggested by
>Carl Ebeling but the book 'All the right moves' in which it appears is now out
>of print and Schaeffer doesn't describe the method himself. He quotes some
>performances around 1.2x to 1.5x bigger than minimal (2.2 for Belle), does
>anyone have any figures for their programs they can share?
>
>Or does anyone have a useful general formula for the size of the minimal tree
>based on a varying bf[depth]?
>
>The figures I obtained during a game with my program playing both sides,
>averaged over the first 18 b/w moves were
>
>ply 3: 1.21x minimal
>ply 4: 2.48x minimal
>
>These actually look very similar to the graph in fig 1 - derived from Phoenix
>-in Schaeffer's paper ('New Advances in alpha-beta searching'). And yet my
>program looks like it doesn't order and prune as well as others and spends
>proportionally longer searching the moves 2-n at each iteration than others.
This will smooth out as you add extensions, refine qsearch and such.
>Ian
If I understand your question right, I think you can do the following.
If you fail high but not on the first node, then all the nodes computed efter
you entered this node and before you searched the fail high node will be wasted
(assuming you don't hash).
Different problem is the PV nodes.
If the best pv move wasn't searched first you will have to research this node
again, this time with pv move first so you get to search the remaining moves
with a narrower window.
This way you can't be sure you get the move that cuts-off the fastest, to find
this you really have to search minimax, to try all moves at every node
regardless if one cuts off fast.
-S.
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