Author: Dave Gomboc
Date: 18:42:09 08/11/00
Go up one level in this thread
On August 11, 2000 at 14:46:22, Christophe Theron wrote: >On August 10, 2000 at 11:06:48, Robert Hyatt wrote: > >>On August 09, 2000 at 16:42:26, Andrew Williams wrote: >> >>>On August 09, 2000 at 16:01:49, Christophe Theron wrote: >>> >>>>On August 09, 2000 at 05:41:22, Andrew Williams wrote: >>>> >>>>>On August 08, 2000 at 15:56:04, Christophe Theron wrote: >>>>> >>>>>>On August 06, 2000 at 16:36:15, Vincent Diepeveen wrote: >>>>>> >>>>>>>Show me an MTD program that uses less nodes a ply as DIEP does. >>>>>>> >>>>>>>What diep is doing is very simple in search: >>>>>>> >>>>>>> PVS (starting with -infinite) >>>>>>> check extensions >>>>>>> checks in qsearch >>>>>>> nullmove R=3 >>>>>>> no other crap. no pruning. Perhaps at WMCC i prune a bit, >>>>>>> but that's because against computers playing is different. >>>>>>> >>>>>>> Yet i'm missing programs using less nodes a ply with MTD. >>>>>>> I"m missing *any* deep searching program that uses MTD actually. >>>>>> >>>>>> >>>>>>Anmon, a french chess program, uses MTD(f). It is a strong program. >>>>>> >>>>>>If you are not pruning in the tree, then MTD(f) should be better for you. I >>>>>>don't use MTD(f) because I use the value of alpha and beta to prune in the tree, >>>>>>and with MTD(f) this kind of pruning makes the search really unstable (you get a >>>>>>fail-high, and when you re-search with a higher window you get a fail-low, >>>>>>oops). >>>>>> >>>>>> >>>>>> >>>>>> Christophe >>>>> >>>>> >>>>>What you can do in these cases is to use the external bounds instead of >>>>>alpha and beta. By "external bounds" I mean the bounds that have been >>>>>established in the mtdf() loop which is driving the alphab-beta search. >>>>> >>>>>Cheers >>>>> >>>>>Andrew >>>> >>>> >>>>Thanks for the idea. >>>> >>>> >>>> Christophe >>> >>>I'd like to claim credit for it, but I got it from a post Don Dailey made here >>>ages ago. >>> >>>Andrew >> >> >>I think that solves the 'lazy evaluation' problem. But I am not sure it is a >>cure-all for pruning based on alpha and beta... > > > >As I understand it is like using an artificial alpha and beta. They would be set >a little bit the way you set alpha and beta for aspiration search, and they are >not changed during the search (at least they stay unchanged for several >re-searches). > >This should adds stability and the behaviour should be close to what you get >with standard alphabeta and aspiration search. > >I have not tried yet, but that's how I understand it. > > > > Christophe They're not really "artificial" by default... these are the established score bounds that your search has determined so far. You can do some guessing and make it a true "aspiration" window if you want to, but that's not required. Dave
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