Author: Robert Hyatt
Date: 20:39:27 03/31/00
Go up one level in this thread
On March 30, 2000 at 13:51:14, J. Wesley Cleveland wrote: >On March 30, 2000 at 01:37:33, Andrew Dados wrote: > >>On March 29, 2000 at 23:50:51, Dave Gomboc wrote: >> >>>On March 28, 2000 at 23:30:11, Andrew Dados wrote: >>> >[snip] >>>>> >>>>>So in the case where there is going to be a fail-low, you think that doing IID >>>>>will use more time than just searching every move immediately at the required >>>>>depth? Why? (If that's not what you meant, then I misunderstood you.) >>>> >>>>That's what I ment, yes. You *have to* search all the moves at that ply to full >>>>depth anyway, so searching first to depth 1, then 2, etc is not helpful at all >>>>in FL node. You'll waste all those nodes. >>> >>>"not helpful at all"? IID will give you better move ordering than you could get >>>statically, which should save you work overall. >>> >> >>Just curious... what 'better move ordering' in FL node? Any move ordering is as >>good as other there (we will search all moves and all will fail low)... and that >>was my main point. >> > >If you *know* it is a FL node, you don't need to search at all. ;) In those >cases where it actually isn't, you need to order your moves to find the >refutation. Yes, but at the fail low node itself, move ordering is totally unimportant. See "An analysis of alpha/beta pruning by Knuth/Moore" if you search a tree to depth=N, then throw everything away after isolating some fail-low nodes, and research the tree to the same depth, with _no_ move ordering at the fail-low nodes, you will search exactly the same tree. _exactly_. Hashing will modify this a bit for random reasons... but at a so-called ALL node (Knuth's terminology) move ordering makes no difference. At each node _below_ an ALL (fail-low) node, move ordering is _critical_ because there you might get away with searching just one move, rather than several.
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