Interesting null-move test

[hgm]

Let me get ths straight:

You use plain null move, no verification? So if you end up in KRK, it is now a draw. And if you end up in things like KRPKR it becomes almost impossible to win, as the opponent would simply sac his Rook for the remaining Pawn, and you would not know how to checkmate him with a Rook up.

Most won Pawn endings would also be bungled; KPK is no longer a win if the passer is not out of reach.

Seems to me that this should cost you quite a bit more than 2 Elo. Rook endings are very common (> 10% ?), and not being able to win any of those should at least cost you a few percent in score, and each % corrsponds to 7 Elo. So a 20-50 Elo drop would have to be expected.

The test must be flawed somehow...

[Desperado]

Let me get ths straight:

You use plain null move, no verification? So if you end up in KRK, it is now a draw. And if you end up in things like KRPKR it becomes almost impossible to win, as the opponent would simply sac his Rook for the remaining Pawn, and you would not know how to checkmate him with a Rook up.

Most won Pawn endings would also be bungled; KPK is no longer a win if the passer is not out of reach.

Seems to me that this should cost you quite a bit more than 2 Elo. Rook endings are very common (> 10% ?), and not being able to win any of those should at least cost you a few percent in score, and each % corrsponds to 7 Elo. So a 20-50 Elo drop would have to be expected.

The test must be flawed somehow...

if so.
you should also think of the possibility, that many more decisions are done closer to midgame positions.(which may get back these 20-50 elos you mentioned).

Michael

[hgm]

In middle-game positions all the versions use null move, there is no difference there. So how could you gain anything back?

[Desperado]

What i mean is, if you search, and drop into KrK for example at ply 15 you will handle ply 16,17,18... much quicker, saves time,saves resources (just a thought).

That doesnt mean that you finally end in the KrK,where you must handle
it, and as long you dont have to outplay the position there maybe a gain.

So it maybe interesting to switch between outplay-position vs. position
visited by the search only.

On outplaying such types of positions someone can use verification or the 1-piece condition. Having such a position only in the search space one can use simply _plain null_.(we only want to reach the position as idea).

maybe my logic is flawed now

Michael

[Uri Blass]

Let me get ths straight:

You use plain null move, no verification? So if you end up in KRK, it is now a draw. And if you end up in things like KRPKR it becomes almost impossible to win, as the opponent would simply sac his Rook for the remaining Pawn, and you would not know how to checkmate him with a Rook up.

Most won Pawn endings would also be bungled; KPK is no longer a win if the passer is not out of reach.

Seems to me that this should cost you quite a bit more than 2 Elo. Rook endings are very common (> 10% ?), and not being able to win any of those should at least cost you a few percent in score, and each % corrsponds to 7 Elo. So a 20-50 Elo drop would have to be expected.

The test must be flawed somehow...

I think that it is not clear that Crafty cannot win KRK with null move turned on always.

I can imagine the following possibilities
1)tablebases are used so Crafty wins easily.

2)Even without tablebases the correct moves have a threat(the question if they have a threat or not is dependent on the evaluation function) so they are not pruned.

[Desperado]

What i mean is, if you search, and drop into KrK for example at ply 15 you will handle ply 16,17,18... much quicker, saves time,saves resources (just a thought).

...
Michael

So if you drop frequently from a late midgame position into these
kind of endgame positions, isnt it possible you will gain a ply for the midgamePos ?

[hgm]

No way you would gain much from this. So close to the leaves the null move cannot buy you much reduction anymore. And even if it would significantly reduce the number of nodes you need, you get that at the expense of the score being unreliable, because you would have missed all zugzwangs. If that helps, you migt as well return a random score without any search, if you get into a position where you would normally switch off null move.

[metax]

I just thought about this and enabled null-move everywhere in ChessMind just for a KRK test. The thesis that it wouldn't be able to win KRK is just not true and I even think about enabling null-move just for these endings (KRK, KQK etc.) because it is able to mate _faster_ with null-move than without.

edit: In KRPKR the opponent would, of course, never sac his rook for the pawn so that example is unrealistic.

[hgm]

I think that it is not clear that Crafty cannot win KRK with null move turned on always.

I can imagine the following possibilities
1)tablebases are used so Crafty wins easily.

Well, that is what I define as 'flawed'. If you want to study the effect of not switching off null move, and then bias the sampling to exclude most cases where you would have to switch off null move, by looking them up in a tablebase rather than searching them with null move on, the test was meaningless from the beginning.

The same would hold if the opponents would resign in KRK, not knowing that Crafty isn't able to win that anymore.

2)Even without tablebases the correct moves have a threat(the question if they have a threat or not is dependent on the evaluation function) so they are not pruned.

Unless white finds a quick mate by sheer accident in one of the first lines it searches, it will never be able to improve on these lines. It is almost always possible fr black to do better (i.e. not being driven towards the edge/corner so fast) by injecting some null moves in zugzwang positions. So no matter how hard white tries, he will never be able to find an improvement on a line he already has. Even when he tries the correct moves, black will refute them by cheating.

[metax]

Sorry, what I just said about the null-move version being better was not true. In a KRK position that was mate in 15 according to the tablebases the version without null-move could mate in 16 moves when I played the optimal tablebase moves. The version with null-move mated in 19 moves. Nevertheless it _could_ win the endgame but was slower than the version without null-move.