"-alpha - 1" vs "-beta" as alpha value in LMR

[KhepriChess]

What I mean:

Code: Select all

negamax(depth, -alpha - 1, -alpha)

versus

Code: Select all

negamax(depth, -beta, -alpha)

There seems to be little consistency in engines between which is used when. I've looked at a number of engines, and some the use of one over the other seems to vary quite a bit. Some will use one for all reductions, others will use it only in more limited cases. Or use one in all cases if a reduction fails or only in a pv-node (or non-pv node) fails.

Is there an actually correct use of one over the other?

[Bo Persson]

If you search with a minimum window, beta will be alpha + 1. So no difference.