michiguel wrote:jdart wrote:bob wrote: I see no reason to treat PV vs non-PV nodes any differently. That is a bad misconception. Why would you want to search the PV one way, and then search the other moves another way?
I suspect avoiding transposition table cutoffs in the PV became popular due to its use in Fruit. It doesn't make a lot of sense to me either.
I think that for an engine that is used for analysis is the way around: It does not make any sense to gain almost nothing in terms of search speed and lose the PV, which is a valuable piece of information. People are crazy about gaining 1 elo point and forget how a true chess player may use the engine.
Miguel
But Fruit also uses other PV-dependent techniques for example, different extensions in full nodes vs. zero-width nodes. I think the general idea is that you are going to cut most of those nodes anyway, so you cut the tree size a bit. If the search throws up anything really interesting that node will get re-searched with the full extensions. A bit like LMR but playing with the extensions. This is now done in quite a few strong programs.
I think those are important reasons, for me at least and Miguel's remarks are not technical, so not much dispute about that.
Another simple reason why PV- nodes and Non PV nodes are different; not that this is required per sé, but usually PV nodes will be searched by Aspiration window search, and Non PV nodes will be searched by a Null window search.
● The characteristics of these searches being -very?- different, this is more important than the other mentioned changes. It is not so much about treating the nodes differently, it is about the different types of search.
● Aspiration window search under circumstances sometimes can be very costly compared to Null window search. But this is usually offset by much smaller number of PV nodes. You can afford other costly measures better in PV nodes.
● In my view all the other differences are just ways of making these two types of searches work together better.
That does not mean any of the different ways of handling PV nodes and Non PV nodes -in Stockfish or other programs- are
all necessary, or even
any of them, but it just makes sense that PV nodes will be more valuable, otherwise they would not be PV nodes. There is nothing mysterious about that, I'm not claiming having new insights here but it is also no 'misconception'. In my humble opinion
Eelco