H. G. Muller wrote on Tue, Jan 2, 2018 07:35 PM UTC:
@Greg: In WinBoard I distinguish two cases: official game end due to impossibility of help mate, and adjudication because of practical impossibility to force a mate against reasonable couter play. KNK and KBK (or more Bishops on the same shade) are official draws, KNNK, KBKN, KRKR are just impossible to win. For the latter type there usually are some tactical positions from where they could be lost (like mate in 1, or Rook capture in 3), so WinBoard does the adjudication (when enabled) only after a few moves. Note that FIDE rules also stipulate draws in some positions no engine or GUI would recognize, with impenetrable walls of Pawns separating the Kings and the pieces that could attack them.
To apply these rules to arbitrary fairy pieces requires kowledge that is not so trivial to obtain automatically, but usually easy to provide as part of the game definition. For orthodox Kings the possibility for help mates exists with single pieces that attack orthogonally adjacent squares, or any two pieces not bound to the same color. But for more general royal pieces it can be tricky. E.g. in Knightmate a Bishop superficially can cause a checkmate (Royal Knights on a1 and d4, Bishop on b2), but the position is unreachable from any 3-men position. To know if a mate can be forced would require generating a 3- or 4-men EGT. Sometimes you quickly see that the mate cannot be forced in general (such as with a pair of Knights or a Gnu), sometimes you have to calculate for many moves (e.g. KQKQ or Wazir + Ferz). But perhaps piece combinations where forcible mates can take many moves should never be adjudicated as draws.
@V.Reinhart: EGTs are always created by retrograde analysis. Doing this for a single 7-men end-game can take weeks. Each extra men basically drives up the storage requirement a factor 64 (32 if it is a color-bound piece), for standard 8x8 boards, and the generation time likewise. 4-men on 8x8 take only a second, however, and 5-men less than a minute, and can conceivably be done during a game.
There is a trick, however: these estimates only apply to pieces that have access to the full board, through reversible moves. Orthodox Pawns can only move forward, and the number of different Pawn constellations with 5 or 6 Pawns that are mostly blocking each other head to head can be surprisingly low. So in principle it should be easy to generate EGTs for Kings + 2 mobile pieces + a number of Pawns, even if the total number of men would be 6-10, during the game, provided the Pawns are sufficiently blocking each other. The point is that you only have to worry about the Pawn constellations that are still reachable.
@Greg: In WinBoard I distinguish two cases: official game end due to impossibility of help mate, and adjudication because of practical impossibility to force a mate against reasonable couter play. KNK and KBK (or more Bishops on the same shade) are official draws, KNNK, KBKN, KRKR are just impossible to win. For the latter type there usually are some tactical positions from where they could be lost (like mate in 1, or Rook capture in 3), so WinBoard does the adjudication (when enabled) only after a few moves. Note that FIDE rules also stipulate draws in some positions no engine or GUI would recognize, with impenetrable walls of Pawns separating the Kings and the pieces that could attack them.
To apply these rules to arbitrary fairy pieces requires kowledge that is not so trivial to obtain automatically, but usually easy to provide as part of the game definition. For orthodox Kings the possibility for help mates exists with single pieces that attack orthogonally adjacent squares, or any two pieces not bound to the same color. But for more general royal pieces it can be tricky. E.g. in Knightmate a Bishop superficially can cause a checkmate (Royal Knights on a1 and d4, Bishop on b2), but the position is unreachable from any 3-men position. To know if a mate can be forced would require generating a 3- or 4-men EGT. Sometimes you quickly see that the mate cannot be forced in general (such as with a pair of Knights or a Gnu), sometimes you have to calculate for many moves (e.g. KQKQ or Wazir + Ferz). But perhaps piece combinations where forcible mates can take many moves should never be adjudicated as draws.
@V.Reinhart: EGTs are always created by retrograde analysis. Doing this for a single 7-men end-game can take weeks. Each extra men basically drives up the storage requirement a factor 64 (32 if it is a color-bound piece), for standard 8x8 boards, and the generation time likewise. 4-men on 8x8 take only a second, however, and 5-men less than a minute, and can conceivably be done during a game.
There is a trick, however: these estimates only apply to pieces that have access to the full board, through reversible moves. Orthodox Pawns can only move forward, and the number of different Pawn constellations with 5 or 6 Pawns that are mostly blocking each other head to head can be surprisingly low. So in principle it should be easy to generate EGTs for Kings + 2 mobile pieces + a number of Pawns, even if the total number of men would be 6-10, during the game, provided the Pawns are sufficiently blocking each other. The point is that you only have to worry about the Pawn constellations that are still reachable.