null move when to start it

[adams161]

hi,

I have a condition not to do a null move if *both* alpha or beta are not set.

on the first move at the root when it gets to depth -1 or second ply of the search both alpha and beta are not set so it wont do a null move.

but what i realized is once there is a root alpha, whenever it tries any moves at the root and gets to teh second level of search, ply 2 or depth -1 , alpha will never be set. beta will be but not alpha.

Should i not do null moves at the rootdepth-1 or should i do null moves even if alpha is not set but beta is.

Mike

[bob]

hi,

I have a condition not to do a null move if *both* alpha or beta are not set.

on the first move at the root when it gets to depth -1 or second ply of the search both alpha and beta are not set so it wont do a null move.

but what i realized is once there is a root alpha, whenever it tries any moves at the root and gets to teh second level of search, ply 2 or depth -1 , alpha will never be set. beta will be but not alpha.

Should i not do null moves at the rootdepth-1 or should i do null moves even if alpha is not set but beta is.

Mike

1. You can do null move at _every_ node with hardly any penalty and it will be a big win over no null-move at all.

2. you can get a bit more clever and not do null-move except when beta - alpha == 1, and get a slightly bigger win although the difference is not very significant.

You can also use the hash table to disable null-move. For example, if you find an entry that says "fail low but draft is not sufficient to do so" then a reduced depth search will likely fail low and the hash hint would avoid trying the null-move. Again the gain is not huge...