Author: pete
Date: 13:28:05 08/09/00
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On August 09, 2000 at 12:36:44, Eran wrote: > >When my Fritz6a began to stage the engine tournament, a message appeared and >said, "Fail High!". At the same time, my computer strangely wrote to the hard >disk from time to time. I did not know whether my computer would do it >indefinitely. 1.) The writing to your hard disk : This might be of no meaning at all : maybe you saw a few blinks from your hard disk lights and as you were already expecting something really weird from this wicked "Fail High" you thought it was some bad threat to your computer's sanity . But if it _really_ was using HD a lot it is a clear sign of another problem which has nothing to do with "failing" . One adjustable option of most chessprograms is the "Hashtable" . Results of previous searches are stored here to spare some time while examining the position when they are met again by a simple look-up in those tables when else you would have to search them again . The memory you can use for this is for sure limitted by the total RAM you have in your computer ; and if you play a tournament with two programs on one computer it also has to be divided between two programs . A conservative setup would be to save half of the memory for the internal work your computer has to do just to stay alive and to share the rest of the memory evenly between the contestants . So if assumed you have 64MB RAM in your computer , leave 32MB for your operating system and what do you have left ? 16 MB "Hash" for each program participating in the tournament . Now if you give say 64 MB Hash to Fritz what can it do ? It simply isn't availlable ; so it is "paging " ; this means it can't find memory in RAM and so it has to use space on the hard disk instead . This is really a bad idea as accessing HD is terribly slow . Get the idea ? Your program will be "failing" alot as you slowed it down that much by a too optimistic setup ( this is a little simplified as I suspect there isn't any real problem here anyway but a thing you should be ( and probably are anyway ) aware off . > >What is "Fail High!"? Is that bad? Is something wrong with Fritz6a? Since I am >not a programmer, please explain that to me very clearly. 2.) "Fail High " isn't anything bad at all . In fact it is quite the opposite : it is really marvellous ! A "Fail High" is meaning the following : While searching deeper and deeper you ( as a chessprogram ) always have the results of your previous search in mind , and if you go one step deeper you make an assumption of the evaluation you can expect ( this is one lower-bound ( alpha) and an upper-bound ( beta ) And now what happens ? Hey : you get an evaluation which is _way_ higher than this "beta" : isn't it cool ? So you "fail high" ; in fact you didn't fail at all , but in a sense you failed predicting the real value for the position : you simply were too pessimistic :-) ! Fritz' talking is simplistic as it ( by now ) doesn't have any intelligence at all ; it _does_ know a few "chessic" ( lol ) terms and when it detects them it will babble about them .. So _whenever_ it detects a backward pawn it will say : "I can handle backward pawn !" even if it doesn't have _any_ impact on the position at all . Same it is with the "Fail High" and the bad thing : the "Fail low " ( I am sure you already understand this one by now ) ; it will proudly talk about it like it had something important to say , and this is the reason your Fritz will probably talk about this "fail high " quite often until you finally disable its chatting or you are Mr Kasparov himself :-) > >Thanks in advance. >Eran I am definitely sure this is not a super-technical answer as I don't have any idea about teaching a computer how to play chess , but this unfortunately also means you have to take my answer with a grain of salt ;-) Cheers. pete
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