Syzygy Tablebases without rtbz (distance to zero) files cause wrong endgame moves

[ljgw]

FrankWalter 2.3.5 will play the wrong move in this situation: 8/8/8/8/3K4/6r1/4k1p1/6R1 b - - 7 82 when it has access to Win-Draw-Loss tablebase files, but not the Distance-to-Zero files because it relies on these DTZ files too much.

This also causes weird looking moves in the endgame where the winning distance to zero move is giving pieces away.

Solution is to select all moves (taking the 50 move rule into account) that get the maximum result (win or perhaps draw) in a root position and only consider these in the search. Make sure that the WDL information is not terminating the search on ply one.

[ljgw]

workaround

As a work-around: please make sure you have the corresponding .rtbz files for any .rtbw syzygy file you have. If you do not have them, it might be better to not provide syzygy tablebases to FrankWalter.