Author: Vincent Diepeveen
Date: 11:17:57 05/28/04
Go up one level in this thread
On May 27, 2004 at 11:57:33, Vasik Rajlich wrote: >On May 27, 2004 at 11:22:40, Vincent Diepeveen wrote: > >>On May 27, 2004 at 06:39:23, Vasik Rajlich wrote: >> >>>On May 26, 2004 at 13:49:38, Tord Romstad wrote: >>> >>>>On May 26, 2004 at 13:34:23, Robert Hyatt wrote: >>>> >>>>>I have used "IID" for years, but in a very restricted way, namely to handle the >>>>>case along the PV where I have no hash move. I've never tried it _everywhere_ >>>>>before, so have no data. But I intend to try to see if it is something that >>>>>could work, or if it is a waste... >>>> >>>>I am fairly sure you will find that _everywhere_ is a waste. It is probably >>>>not worth doing near the leaf, you have a hash table move to search, or when >>>>a fail-low is most likely. Perhaps you should also use a somewhat bigger >>>>reduction factor than in your "along-the PV IID". >>>> >>>>Note that it could also be interesting to look for good ways to make use of the >>>>return value of the internal search. It gives a reasonably reliable estimate >>>>of the value of a full-depth search, and can be useful as an ingredient in >>>>pruning tricks. The most obvious (and entirely risk-free) case is when the >>>>reduced-depth search returns a mate score. When this happens, it is clearly >>>>not necessary to do a full-depth search. >>>> >>>>Tord >>> >>>Yes, there is lots of room for playing with IID. >>> >>>Note that 95% of all nodes fail high in some way, so you can be pretty >>>aggressive. >> >>that sounds very high. > >Ok - just checked - it's more like 93-94%, and I'm doing MTD (f). mtd versus pvs is rather irrelevant for this IMHO. More important is whether you do pruning in whatever form last few plies. It's not amazing to me that MiT guys go MTD by the way :) I bet you like opteron. MTD must use hashtable everywhere, also in qsearch. How much does it speed you up the opteron/a64 ? >> >>>The IID principle can also apply to some additional situations: >> >>>1) You have a hash move, but it's at depth-2 rather than depth-1. You can do >>>another IID layer in this case. >> >>In that case hashmoves works better of course. >> >>>2) Your fail-high hash move (for some engines the only possible kind of hash >>>move) fails low. Here you can do IID to get an alternative move. >> >>This is highly unlikely as your IID is at depth-i where i > 0. >> >>So most likely that hashmove is already from a position j >= depth - i, which >>makes IID a complete waste of your time. > >I meant an IID where the move that already failed low is thrown out. You want >the second-best move at the reduced depth. Use double nullmove. works better than IID and the first move you already get the best move :) >Usually, you will waste a few nodes this way of course. The idea is to avoid-the >worst case scenario - of doing a full search through a bunch of other moves, >before finding the fail-high move. You can add 1000 conditions, but if something doesn't work in general, it won't work with 1000 conditions either. It just is harder to test in a way that objective and statistical significant conclusions are possible to statistical significant conclude whether it works or doesn't. >> >>>And - as Tord mentioned - an IID search can be turned into the final >>>reduced-depth search, based on its result. >>>Vas >> >>Depth reducing the current search? >> >>Sounds like a rather bad idea to me. > >Well that's the million dollar question, isn't it? Seems there is 2 camps. I'm currently in the camp that i tried both worlds and concluded that depth reducing with nullmove is already enough. I can imagine last few plies some types of forward pruning somehow work. So far i could not prove that last though. I have a hard time believing that forward pruning in the entire tree is going to beat the nullmove pruning. We both are titled chessplayers, and i see simply that the few mistakes todays engines make, usually it is a dubious move caused by bugs in the forward pruning. Shredder is clearest example. >Vas
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