PLY vs 1

[outAtime]

Just wondering why some programs are defining PLY as some number like 16 or 60 (I suppose any number would do, as long as it can be evenly divided by two) and then making sure it is = to the (extension) number, which Ive seen also getting strange numbers assigned, such as 45 or 60, depending on the type of extension. This must have a good reason, but for someone who has only played with algorithms like (depth-2) for example, something like (depth-2*PLY) seems strange indeed. What is the difference between (depth>5) and (depth>5*PLY) if PLY = 16? . Thanks. I figure there must be some kind of good reason to define all these things like this, I just can't figure out why. Seems like alot of re-definitions in some of these programs!

[Daniel Shawul]

I hope i am the first to answer this simple question It is called fractional extensions. The idea is to extend by fractions of a ply instead of a _full_ ply to avoid tree explosions which can be caused by a series of check + single reply exte1nsions for example. You can find tons of information on talkchess.
cheers
Daniel

[outAtime]

Thanks