Author: blass uri
Date: 01:14:13 10/05/99
Go up one level in this thread
On October 04, 1999 at 22:37:48, Robert Hyatt wrote: >On October 04, 1999 at 20:33:35, blass uri wrote: > >>On October 04, 1999 at 18:46:11, Robert Hyatt wrote: >> >>>On October 04, 1999 at 14:17:06, blass uri wrote: >>> >>>>On October 04, 1999 at 11:52:43, Robert Hyatt wrote: >>>> >>>>>On October 04, 1999 at 10:30:40, blass uri wrote: >>>>> >>>>>>On October 04, 1999 at 09:41:30, Robert Hyatt wrote: >>>>>> >>>>>>>On October 04, 1999 at 04:26:17, blass uri wrote: >>>>>>> >>>>>>>>On October 03, 1999 at 23:44:31, Robert Hyatt wrote: >>>>>>>> >>>>>>>>>On October 03, 1999 at 23:17:29, Ricardo Gibert wrote: >>>>>>>>> >>>>>>>>>>[snip] >>>>>>>>>>> >>>>>>>>>>>my webster's defines 'sacrifice' as 'voluntarily giving up something of >>>>>>>>>>>value'. I have a hard time saying 'I will sacrifice a ten-dollar bill if >>>>>>>>>>>you will give me a 20 dollar bill in return...' >>>>>>>>>>> >>>>>>>>>>>:) >>>>>>>>>> >>>>>>>>>>Ok, you got me. I neglected to explicitly state I was refering to the _chess_ >>>>>>>>>>version of the term. >>>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>then here is a 3-move sequence. Sacrifice or combination? >>>>>>>>> >>>>>>>>>RxB, NxR, RxN. >>>>>>>>> >>>>>>>>>RxB obviously dumps a rook for a knight. or if you look to the end of the >>>>>>>>>combination it wins two pieces for a rook which is a significant advantage. >>>>>>>>> >>>>>>>>>Sacrifice or combination? >>>>>>>>> >>>>>>>>>How is that different from QxP+, RxQ, RxR#?? >>>>>>>>> >>>>>>>>>Dumping a queen for a pawn? Or winning the king? >>>>>>>>> >>>>>>>>> >>>>>>>>>>> >>>>>>>>>>>But I don't object to the term being used.. I just think that for a computer, >>>>>>>>>>>the concept 'sacrifice' is wrong. It is just a perfectly computable >>>>>>>>>>>combinational tree search... >>>>>>>>>> >>>>>>>>>>You can give up a bishop to obtain a draw by perpetual check and because you >>>>>>>>>>never get the material back, it is a called a sacrifice. I know it seems trivial >>>>>>>>>>and is not what people generally have in mind when they use the term >>>>>>>>>>"sacrifice", but I do believe it's use in such cases is fairly universal. >>>>>>>>> >>>>>>>>> >>>>>>>>>in the case of a computer, it isn't 'sacrificing'. It _sees_ that it can >>>>>>>>>draw or that it can win. IE it isn't giving up _anything_. A human might >>>>>>>>>toss a bishop 'thinking' (but not sure) than he can force a perpetual. But >>>>>>>>>a computer either 'proves' that it can force it, or it won't ever go for the >>>>>>>>>move in the first place. >>>>>>>> >>>>>>>>Not truth. >>>>>>>> >>>>>>>>Some programs use also selective search. >>>>>>>>I believe that Fritz evaluates positions based on some average between >>>>>>>>The evaluation based on selective search and the evaluation based on brute force >>>>>>>>search. >>>>>>>> >>>>>>>>If the selective search show perpetual check and the brute force does not see it >>>>>>>>then Fritz (in a bad position) might 'think' that he have chances to do a >>>>>>>>perpetual check without proving it and play for it. >>>>>>>> >>>>>>> >>>>>>> >>>>>>>However, that is a _bug_ and not a _sacrifice_ because the program searched and >>>>>>>found the perpetual. Even though it was wrong. But the _search_ said draw, and >>>>>>>the tree it searched 'proved' to the program that it was a draw. Unfortunately, >>>>>>>if this is the way Fritz searches (I don't believe it does this personally, >>>>>>>because it would be so horribly inefficient to do both kinds of search, that >>>>>>>Fritz would not be nearly as tactically strong as it is today) then the sac is >>>>>>>the result of a bug, not because of a computer 'speculating'... >>>>>> >>>>>>I know that Fritz is speculating and it is not a bug. >>>>> >>>>>Sorry, but I don't believe that. It either searches and 'sees' something >>>>>or it searches and 'doesn't see' something. I know of no algorithm that can >>>>>just 'guess' at a result, and fold this into the alpha/beta search along with >>>>>a normal deep null-move search, and then somehow combine those two different >>>>>results. >>>> >>>>The fact that you do not know does not prove that it does not exists. >>>> >>>>I also do not know if it exists and only guess because I had no explanation to >>>>some strange behaviour of the evaluation function that I saw(not often). >>>> >>>>It is possible that this strange behaviour is a bug >>> >>>I don't "know" that fritz doesn't do this either. That is why I clearly >>>wrote "I don't believe...." which is quite different from saying "It >>>absolutely does not..." >>> >>>>> >>>>>IE CSTal doesn't 'speculate' in that form... it just has large positional >>>>>scores it tosses into the mix when it sees certain things going on on the >>>>>board, such as the king too exposed or whatever. And deep/fast searchers >>>>>generally are able to spot the fatal flaw in such speculation and pounce on >>>>>it with both feet. I have _never_ seen Fritz behave in this manner because if >>>>>it did, it would get crushed by programs that didn't behave like that... >>>> >>>>It is possible that usually the selective search does not lead to mate so the >>>>number of the selective search does not have big influence on the evaluation >>>>function. >>>> >>>>If you use 0.08*selective search score+0.92*brute force search score >>>>then you will see problems only when the brute force search score leads to mate. >>>> >>> >>> >>>But who does _both_ and merges the scores together? That is the part that makes >>>no sense from a tree-searching point of view. Because the two search spaces >>>overlap a _lot_ and it is a lot of wasted effort... >>> >>> >>> >>>>You also can use a different formula that is not linear. >>>>> >>>>> >>>>> >>>>> >>>>>> >>>>>>In a case the selective search show draw by perpetual check and the brute force >>>>>>search does not see it the evaluation is probably going not to be 0.00 but >>>>>>something between 0.00 and the evaluation of the brute force search. >>>>>> >>>>> >>>>> >>>>>Again, I don't believe that fritz is doing _two_ searches, one selective and >>>>>one non-selective. It might be adding some selectiveness on to the end of the >>>>>normal search, as that has been done as far back as the original greenblatt >>>>>program... However, Thorsten has reported seeing lots of 0.00 scores when they >>>>>are simply wrong. I have played fritz on the servers and had the opponent say >>>>>"I am seeing a draw" while Crafty was seeing +3.00, and in many cases, the 0.00 >>>>>was wrong... >>>>> >>>>> >>>>> >>>>> >>>>>>I do not remember cases of speculating perpetual but I remember cases of >>>>>>speculating when it saw a win for itself in some selective lines and decided >>>>>>to do a sacrifice(sometimes it may be right sacrifice and it also may be >>>>>>a wrong sacrifice). >>>>>> >>>>>>I guess that it does an everage between selective search and brute force >>>>>>because I saw some evaluations that I can explain only by this theory. >>>>>> >>>>>>I remember a case when the evaluation started to go down slowly from a big >>>>>>advantage for white 7-8 pawns towards no advantage and >>>>>>The sequence of evaluations was arithmetic sequence. >>>>> >>>>> >>>>>that happens. It simply means that the evaluation is grossly faulty, or that >>>>>the search is faulty... we all have that problem from time to time... I have >>>>>lost +5 games on ICC and won -5 games, against computer opponents.. >>>> >>>>I remember an evaluation that cannot be explained by the position >>>> >>>>It started from +8 or +5 (I am not sure about the exact number and got down by >>>>0.31 every iteration(again I am not sure about the exact number) >>>> >>>>evaluation like +3 pawns could not be explained by a logical evaluation >>>>because if you see that you win the queen it should be at least +8 pawns and if >>>>you do not see it because of null move problems the evaluation should be close >>>>to 0. >>>> >>>>Uri >>> >>> >>>Not necessarily... you can hold off such losses at times by giving up a bit of >>>positional compensation.. a sort of 'positional horizon effect'. But each >>>iteration takes you a ply deeper and you have to give up more to hold the >>>loss beyond the horizon... and down, down, down goes the eval... >> >>The relevant position is: >> >>7k/4K2p/7P/3p4/8/4Q3/1q6/8 w - - 0 1 >> >>The first evaluation above 0 of Fritz5 is +5.16 pawns for white >>I do not believe that it can be explained by positional compensation. >> >>If it is because of a bug then Fritz3 and Fritz4 have the same bug(I do not know >>if Fritz5.32 shows similiar behaviour) >> >>Uri > > >are you sure this is the position? This seems to be a mate in 8 according >to my PII/300 notebook (crafty): > > 9 4.89 0.48 1. Ke6 Qa1 2. Kd7 Qa4+ 3. Kd6 Qb4+ > 4. Kxd5 Qb7+ 5. Kc4 Qa6+ 6. Kb4 Qd6+ > 7. Kb5 Qd5+ 8. Kb4 <HT> > 9-> 7.46 0.48 1. Ke6 Qa1 2. Kd7 Qa4+ 3. Kd6 Qb4+ > 4. Kxd5 Qb7+ 5. Kc4 Qa6+ 6. Kb4 Qd6+ > 7. Kb5 Qd5+ 8. Kb4 <HT> > 10 8.27 ++ 1. Ke6!! > 10 12.34 Mat08 1. Ke6 Qa1 2. Qb6 Qe1+ 3. Kd7 Kg8 4. > Qf6 Qg3 5. Qe6+ Kh8 6. Qe8+ Qg8 7. > Qe5+ <HT> > 10-> 18.59 Mat08 1. Ke6 Qa1 2. Qb6 Qe1+ 3. Kd7 Kg8 4. > Qf6 Qg3 5. Qe6+ Kh8 6. Qe8+ Qg8 7. > Qe5+ Qg7+ 8. Qxg7# <HT> > 11 23.23 Mat08 1. Ke6 Qa1 2. Qb6 Qe1+ 3. Kd7 Kg8 4. > Qf6 Qg3 5. Qe6+ Kh8 6. Qe8+ Qg8 7. > Qe5+ Qg7+ 8. Qxg7# > 11-> 36.33 Mat08 1. Ke6 Qa1 2. Qb6 Qe1+ 3. Kd7 Kg8 4. > Qf6 Qg3 5. Qe6+ Kh8 6. Qe8+ Qg8 7. > Qe5+ Qg7+ 8. Qxg7# > 12 50.03 Mat08 1. Ke6 Qa1 2. Qb6 Qe1+ 3. Kd7 Kg8 4. > Qf6 Qg3 5. Qe6+ Kh8 6. Qe8+ Qg8 7. > Qe5+ Qg7+ 8. Qxg7# I am sure that it is the position and I believe that the reason that Fritz cannot see the mate is that it is a null move problem for Fritz. 1.Ke6 threats nothing. Try the position after Ke6 with white to move. Uri
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