Author: David Blackman
Date: 23:12:01 05/07/98
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On May 08, 1998 at 00:45:59, Howard Exner wrote: >I've read here and on RGCC that some programs using something called >pre-processing. Could someone explain what this is? > >What programs use pre-processing? >What are the basic pros and cons? The general idea is that you do a careful positional analysis at the base of the tree, and use the results to fill a piece/square table of the positional value of each piece on each square. Then when you need a positional value at a leaf node, you just add up the piece/square values for all the pieces. Actually it can be even faster than that if you incrementally update the sum of the values as you climb through the tree. The advantages are that you can do a comparatively sophisticated positional analysis because you only have to do it once per search, and you can get very fast searching because you don't do much work at the leaf nodes. The disadvantage is that by the time you get to the leaf nodes and use the piece/square tables, they are often out of date. For instance the analysis at the base of the tree might indicate a pawn weakness on a given square, and give bonuses for pieces to attack that square, but by the time you get to the leaves, the pawn weakness may have disappeared, but the pieces still want to attack it. Some programs are believed to use a hybrid approach with some analysis done by the preprocessor at the base of the tree, and other features evaluated fully at the leaves. One reasonable compromise might be to evaluate king safety and pawn structure at the leaves (there is a clever way to do this fast) and use piece/square tables and preprocessing for the rest. Fritz is rumoured to be a pre-processor. Anything else that goes that fast probably is too. Crafty isn't, or at least not much.
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