Author: Uri Blass
Date: 03:26:58 04/21/04
Go up one level in this thread
On April 20, 2004 at 19:57:00, Sune Fischer wrote: > >>>In principle it can work, but you must be very accurate in guessing when not to >>>nullmove because a full search is very expensive. >> >>I do some static threat detection in my eval. Perhaps this is why this >>works better for me than for you and Tony. > >Yes that could be it, but of course simple tactics can also cause the eval to >estimate completely wrong. > >>Another interesting idea by Sergei Markoff, which didn't work for me the last >>time I tried, but which is used successfully in SmarThink, is to do a shallow >>null move search around alpha before deciding to do the full null move search. >>In pseudo code, it looks like this: > >Interesting, I'll try this out. :) > >>By the way, if you are satisfied with detecting a few of the most common >>mating patterns, and you are willing to accept rare cases of false matches >>(i.e. the static mate detector reports a mate when no mate is there), static >>mate detection is neither very difficult nor expensive. It is not worth >>the cost if you use it only to decide when to avoid null move searches, >>but it is useful when deciding whether or not to search checks in the qsearch. > >I have a simple detector like that, but it is nowhere near perfect. >It might be good enough for this job though, I'll try and fiddle with this some >more, it's on the todo-list, ...somewhere. > >>I used to do static mate detection in the past, but had to sacrifice it when >>I simplified my attack tables. > >As always it's a trade off, your new tables are probably faster? :) > >>>Btw, extending on threats completely blows up the tree for me, it seems there >>>are certain position in the tree where you just have to live with a constant >>>mate threat. Practicly all nodes gets extended here and a blowup is unavoidable. >> >>This is strange. I have very rarely seen something like this. Do you have >>any examples of positions where this occurs? How much did you extend for >>mate threats? > >It happens pretty much in all attacking positions, eg. wac141 takes a lot longer >to solve with null-threat extension on. >I use half a ply for the extension. > >Threat ext ON: >6 -234 13 65536 1.Kf1 Re2 >6 -233 20 126618 1.Qxf4 >6 397 28 188155 1.Qxf4 Bxf4 2.Rxh5 gxh5 3.Rxh5 Bh6 4.Rxh6 Qh2+ >7 981 119 1014524 1.Qxf4 Be7 2.Rxh5 Bxf6 >8 32756 617 6225970 [Mate in 6] 1.Qxf4 Be7 2.Rxh5 Bxf6 3.Qxf6 Qg3+ 4.Kxg3 >gxh5 5.Rxh5 Kf8 6.Rh8++ > >Threat ext OFF: >6 -234 11 52773 1.Kf1 Re2 >6 -233 14 74051 1.Qxf4 >6 321 25 164139 1.Qxf4 Re6 2.Qg5 Rxf6 3.Qxf6 c5 >7 981 66 540949 1.Qxf4 Be5 2.Rxh5 Bxf6 3.Qxf6 gxh5 4.Rxh5 Qh2+ 5.Kxh2 >8 32756 286 2676756 [Mate in 6] 1.Qxf4 Be5 2.Rxh5 Bxf6 3.Qxf6 gxh5 4.Rxh5 >Qh2+ 5.Kxh2 Rxd4 6.Qxf7++ If threat extension does not help you to solve WAC141 at least 1 ply earlier then it means that you probably have a bug in your implementation. I do not have threat extensions today but I believe that they can help when they are done correctly. I believe that not having threat promotion extensions costed movei the game against resp in WBEC. > >I think there are simply too many mates in 1 encountered in the search, most of >them easy to refute and not worth an extension. Tord does not extend every mate threat and if I understand correctly the rule is basically to extend mate threats only if you evaluate the side that threat mate to be the inferior side. Uri
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