Author: Ed Schröder
Date: 09:33:35 10/04/99
Go up one level in this thread
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_ I don't think we should invent new definitions in CC for the word sacrifice. When I replay an annotated game I read it as a chess player not as a chess programmer. A sacrifice is a sacrifice. Ed 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 saw a case in the past when Fritz5(16 bit) did a wrong sacrifice against >>Shredder(I am not sure if shredder2 or shredder3). >> >>Shredder did not find the right defence and Fritz won this game. >> >>Uri > > >That happens... fairly often... you start the _combination_, then half way >into it, a deeper search notices a quiet move by the opponent that is totally >unstoppable, so it can't play to the end of the variation where it calculated >that it gets the material back with interest. I really hate positions where >the search fails high at the last second. I much prefer to find a good tactical >shot early, and then have several iterations to verify that deeper searches >don't find anything wrong with it. It is especially troublesome to see an >early tactical shot start off at +2.7, then the next iteration +2.4, then the >next iteration +1.9, etc. The slope of that function is negative. Will it >continue to drop? dangerous to bet on, but tree searches do it all the time.
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