Author: Ed Schröder
Date: 00:35:04 08/02/98
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>Posted by Howard Exner on August 01, 1998 at 18:48:04: >When analysing positions with Rebel 8 it often happens that the >correct move is locked onto in conjunction with a plus sign appearing >beside the move. eg. Qh6 (+). Chess programmers call this a "fail-high". It means for the move in question that the score is out of the "alpha-beta-window". Therefore the move must be re-searched with a new "alpha-beta-window" to get the correct score for the move in question. >The actual move however can take a long >time before it becomes the first choice among the other move choices. It usually takes a bit longer because of the wider "alpha-beta-window". >Why is there such a long delay in deciding to make this the first choice >when almost always the move turns out to be correct? Did this occur in >Rebel 9 also? Will the new Rebel have that long delay between marking >the move with the plus sign and actually making the move the top choice? In Rebel10 when a "fail-high" or (+) appears Rebel will immediately mark the move as "best-move" and THEN start the re-search to figure out the correct score. This because of the growing popularity of finding key-moves in the so called computer test sets. As far as I know all (most?) chess programs act like this. This change will result in finding key-moves average 20% faster and therefore Rebel10 will perform a little bit better in computer test sets. Still you will notice that sometimes (say in 5% of the cases) the "fail-high" or (+) is NOT rewarded by the "re-search". In this cases Rebel10 will stick to the previous "best-move". I have noticed that other chess programs (all??) do not show this behavior. When they "fail-high" the move always becomes the "best-move". Is the latter true or are there programs around who behave like Rebel in this respect? - Ed -
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