Stupid question about alpha beta and aspiration windows

[cms271828]

Hi, I was looking at the code for aspiration windows on mediocre chess.

It basically says if eval<= alpha or beta<=eval do a full width search starting with the window (-infinity, infinity) at the same depth just searched.

But at the root node, if we start with (-infinity, infinity), then beta = infinity.
But inside this node, we only raise alpha, beta stays the same, so my point is, after the search is done, the alpha beta window in the root node will be (alpha, infinity), so I don't get how we can test if eval is outside of this window.

I must be mixed up somewhere, any advice? Thanks

[Gian-Carlo Pascutto]

Hi, I was looking at the code for aspiration windows on mediocre chess.

It basically says if eval<= alpha or beta<=eval do a full width search starting with the window (-infinity, infinity) at the same depth just searched.

But at the root node, if we start with (-infinity, infinity), then beta = infinity.
But inside this node, we only raise alpha, beta stays the same, so my point is, after the search is done, the alpha beta window in the root node will be (alpha, infinity), so I don't get how we can test if eval is outside of this window.

I must be mixed up somewhere, any advice? Thanks

What you say is fully correct. If you start with -inf,+inf you cannot end with eval outside the window.

[Matthias Gemuh]

Hi, I was looking at the code for aspiration windows on mediocre chess.

It basically says if eval<= alpha or beta<=eval do a full width search starting with the window (-infinity, infinity) at the same depth just searched.

But at the root node, if we start with (-infinity, infinity), then beta = infinity.
But inside this node, we only raise alpha, beta stays the same, so my point is, after the search is done, the alpha beta window in the root node will be (alpha, infinity), so I don't get how we can test if eval is outside of this window.

I must be mixed up somewhere, any advice? Thanks

What you say is fully correct. If you start with -inf,+inf you cannot end with eval outside the window.

(@ colin) ... and that is what you wanted to achieve with the re-search.

Matthias