Author: Mike Hood
Date: 22:24:49 06/27/99
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On June 27, 1999 at 22:06:48, Melvin S. Schwartz wrote: > >On June 27, 1999 at 15:24:33, Gustavo Pereira wrote: > >>I have seen many posts where they say Fritz cannot solve this or that problem. >>Many of the times it is because Fritz is (by default) a null mover. >> >>Now what is the reaction? >> >>Many people start saying that it is because Fritz is not a good program, and >>that you can't switch off the null move engine. >> >>How far from reality!!! >> >>Quoting from the (really meager) Fritz 5.32 manual >> >>'(Selectivity) Denotes the number of plies reduced by the null-move. A value of >>zero means that the null-move is switched off'. >> >>I guess that says it all. > >What effect would changing the default setting to zero have on Fritz's playing >strength? > >Mel This is a theoretical question, probably better left to a chess programmer, but I'll be the first fool to rush in. Many months ago I compared Fritz's performance with different Selectivity settings. The higher the value of Selectivity (6 is maximum), the deeper Fritz searches, ie the more plies it examines in the same time. At Selectivity 0 Fritz doesn't search as deep, presumably because it examines lines it would have ignored otherwise. However, the word "Selectivity" seems to be misleading, because even at Selectivity 0 Fritz seems to be doing some "selection" of lines, it seems to be too fast to be doing a Brute Force search. To put it succintly: the lower the Selectivity value, the less deeply Fritz searches, but the more thoroughly it analyzes. This means that by setting the Selectivity to 0, Fritz might avoid blunders like in the cute little chess problem Kurt quoted, but Fritz could make other errors by not searching deep enough. My guess (here is where I need backup from chess programmers) is that blunders through null move errors are relatively rare. The advantages of deeper searches far outweigh these occasional problems. Speaking practically... Fritz has seven different Selectivity values, from 0 to 6, and Chessbase has made 2 the default. I assume that this value has been proven to produce the optimum playing strength, either experimentally or algorithmically. I'm not sure if a higher Selectivity value brings advantages. Maybe someone can present a position in which "Fritz Sel 6" finds the best move in 10 seconds, whereas "Fritz Sel 2" needs 5 minutes. I'd be glad to hear about it. Mike
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