Author: Michael Neish
Date: 03:29:42 10/19/02
Help! I blew the dust off my program a week ago and started working on it again. I quickly found a problem in the search routine that is causing the program to miss some simple tactics which it really ought to see. I’d be very grateful if someone could give me any comments. Thanks. I think I finally traced the problem down to the way the search routine works. An example is probably best. At root I do a full-width search, with alpha = -MATE, and beta = +MATE for the first move. This returns a value <score>. For subsequent moves I search using the window alpha = (score–30) and beta = (score+30) (purely arbitrary). If the search returns a value <= (score-30) I search again with window –MATE to (score-30), and if it returns a value >= (score+30) I research with alpha = (score+30) to +MATE. I hope this isn’t totally erroneous. Now in a certain position the full-width search will fail high at the root (good score), so it will re-search with the window (score+30) to +MATE, but this actually ends up finding a strong move for the opposite side and returns a fail low second time round. Since the program won’t search any more it will return the value (score+30) thinking it’s got a good position. Then a few moves later disaster strikes. Moreover, it somehow loses track of the PV, but I think this may be a separate problem. Could someone please let me know how to deal with this sort of thing? I'm stuck. Many thanks. Mike.
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