OpenChess

While searching possible moves from a position, we find a move whose score S is greater than or equal to the value of beta. Thus we can disregard the remaining moves from that position, and return a score. It seems that whether we return beta or S (or any number greater than beta) makes no difference, since the position in question will not occur along the principal variation.

Is this correct?

Thanks.

Not quite right ..
its the difference between fail-soft and fail-hard (http://chessprogramming.wikispaces.com/Fail-Soft)

As a result of returning a higher bound you will get tighter bounds on the parent's transposition entries which might improve future searches. Furthermore the null-move mate threat extension requires the fail-soft framework .. should you be interested in trying that.

regards,
Edmund

Edmund wrote:Not quite right ..
its the difference between fail-soft and fail-hard (http://chessprogramming.wikispaces.com/Fail-Soft)

As a result of returning a higher bound you will get tighter bounds on the parent's transposition entries which might improve future searches. Furthermore the null-move mate threat extension requires the fail-soft framework .. should you be interested in trying that.

regards,
Edmund

Not quite right either. Fail-soft framework suggests that you can return score lower than alpha, if a node's best score do not exceeds alpha (fail-low). I know some will disagree, but regardless of the nomenclature, I prefer to consider 3 distinct approaches, in practice, looks like that:
1. Fail-hard - returned result is the upper bound of a node.
2. Fail-soft - returned result is the best score achieved (whether in or outside the window).
3. "? - the one I use" - returned result is at least alpha or the result of the further search (evaluation) of a node if greater than alpha.
Some papers indeed consider the 3th one (which also is the topic's subject) as fail-hard since no value, lower that alpha could be returned, but they are still different.

Mincho Georgiev wrote:lower that alpha could be returned, but they are still different

correction: lower that alpha could NOT be returned, but they are still different.
typo, i apologize.