Author: Guido
Date: 14:33:01 10/04/99
About the possibility of using back moves for a faster generation of endings tablebases, Anthony Bailey on September 19, 1999 wrote: [snip] " I'm interested to know whether ones that work by "unmoving" pieces back from evaluated positions rather than repeatedly moving them forwards from unevaluated positions have been given attention. (I would assume so; given that the average number of ply required to reduce a position is L it would seem to reduce the number of times you have to calculate the legal moves (or "unmoves") in any one position from L to 2. I suspect this is all old ground, but I'm uncertain as to where the best place is to go to catch up; if there are any references available on-line, I'd love to know about them.) " After reading this message, I decided to follow the hint, but I found that saving in cpu time is almost insignificant: depending on the ending, it amounts to some % if applied to the first cycle, when the program is looking for losses in 0 moves and stalemates for both the players. Applying the same procedure to all the cycles, cpu time increases!!! IMO the best solutions consists in applying this procedure only to the first 2 cycles, with a saving not greater than 5-6 % in the best cases (but I have to try more). The reason of it depends on the fact that the program, every time it finds a loss during the nth cycle, calculates the back moves to set victory in n+1 moves, but, with the increase of the cycle number, spends a lot of time in finding positions already solved. In my program introduction of back moves in the usual scheme for TB generation is a very easy job, because nothing has to be changed: _only_when_a_loss is found, it is sufficient to make a call to a function that calculates back moves and set the _victory_in_n+1_ moves in the corresponding bytes. In the successive cycle the program will skip automatically the calculated positions. I introduce a parameter in my command string to choose if back moves must be used or not, and, in the first case, for how many cycles this feature must be on. I imagine that there are better ideas than mine for using back moves. IMO there are no possibilities to use back moves in order to generate losing positions that must be calculated with forward moves. Best regards Guido
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