Author: José Carlos
Date: 06:50:18 01/15/04
Go up one level in this thread
On January 15, 2004 at 02:41:40, Uri Blass wrote: >On January 14, 2004 at 19:48:14, Dann Corbit wrote: > >>On January 14, 2004 at 19:08:10, Uri Blass wrote: >> >>>On January 14, 2004 at 18:25:34, Tord Romstad wrote: >>> >>>>On January 14, 2004 at 16:56:20, Anthony Cozzie wrote: >>>> >>>>>On January 14, 2004 at 16:26:42, Ed Trice wrote: >>>>> >>>>>> >>>>>>> >>>>>>>Have you considered trying MTD(f) instead of PVS? I am not sure it is any more >>>>>>>efficient in practice, but it is easier to code, and has the additional benefit >>>>>>>of making you feel different, original, interesting, intelligent, handsome and >>>>>>>attractive. >>>>>>> >>>>>> >>>>>>Well Aske Plaat would love to hear that :) >>>>>> >>>>>>But doesn't MTD(f) trigger a great deal of researches? I remember trying that >>>>>>once and it bloated the tree. >>>>> >>>>>---- opinion mode on ---- >>>>> >>>>>MTD(f) has two big problems. >>>>> >>>>>1, you ponder the wrong move occasionally because your PVs are less accurate. >>>>>If you are pondering the wrong move 20% of the time that is equivalent to a 10% >>>>>time loss. >>>> >>>>This is not a *big* problem by any stretch of the imagination. It does indeed >>>>happen >>>>that the last few moves of the PV are wrong or missing, but I have *never* seen >>>>as obviously wrong move as the second move of the PV. This does of course not >>>>mean that it never happens, but it is clearly very rare. >>>> >>>>On the other hand, it *does* happen that the PV contains only one move, and >>>>there >>>>is no move to ponder at all. This happens maybe once every 5 or 10 games, but >>>>usually when the game is already won or lost. >>>> >>>>>2, MTD(f) is at its worst when the score is dropping. A fail high in MTD(F) is >>>>>much faster than a fail low (1 child node vs all child nodes). >>>> >>>>This is true. The average branching factor is clearly lower when the initial >>>>direction >>>>of the search is downward. >>>> >>>>>Unfortunately, >>>>>this is when you need your search the most: you are in trouble, and you need to >>>>>make exact moves to win/draw (you might already be lost, but thats just the way >>>>>it goes). >>>> >>>>Most of us extend the thinking time in such situations, and try to avoid making >>>>a >>>>move before the search fails high. >>>> >>>>By the way, there are a few things you could try to solve the problem you >>>>describe, >>>>although I haven't yet tried them. The main idea is to give up quickly if the >>>>search >>>>appers to fail low. The easiest thing to do is to just abort the search if the >>>>first move >>>>at the root fails low, and immediately start a new search with a lower search >>>>bound. >>>> >>>>It is certainly possible to find refinements to this idea, but as I said I >>>>haven't experimented >>>>with it yet. >>>> >>>>>I remember some Zappa-Gothmog games where Gothmog had been searching >>>>>8 ply, got in a tight spot, made a 6 ply search, played a huge blunder, and went >>>>>from -1 to -5 the next move. >>>> >>>>It is quite common that the search depth reached varies a lot from move to move >>>>in Gothmog (a difference of 3 or 4 plies is not unusual), but usually this is >>>>due to >>>>DFP rather than MTD(f). A sudden dramatic drop in search depth usually means >>>>that most of the DFP is disabled for some reason. >>>> >>>>And in general, if you want to knock MTD(f), you really need to base your >>>>conclusions on >>>>something more substantial than games against Gothmog, which undeniably is the >>>>slowest, weakest and most buggy MTD(f) engine known to man. >>> >>>I do not believe it. >>> >>>PostModernist also use MTD and I think that Gothmog is stronger than >>>PostModernist. >>> >>>I did not test Gothmog and my impression is based on results that I read that >>>suggest that Gothmog is at the same level of engines like Ktulu. >> >>I think you underestimate PostModernist. It may be stronger than SOS (often >>considered the strongest MTD(f) engine), and so it is surely one of the >>strongest MTD(f) engines around. > >No >I do not underestimate PostModernist. >Your list suggest that it is weaker than Abrok or Anmon when the list that I >read suggested that Gothmog is stronger than them. >http://www.f11.parsimony.net/forum16635/messages/60395.htm > >I see that you test old SOS. >I am surprised to hear that SOS is often considered to be the strongest MTD >engine. > >I thought that this title is of one of the commercial(Shredder showed stupid >pv's so it may use MTD and I also remembered that the same happened with Fritz) > >I do not know how did you get that PostModernist is one of the strongest MTD >engines in the world. > >I do not know which engines use MTD and I simply mentioned the probably weaker >engine out of the only 2 free engines that I knew to use MTD except >Gothmog(PostModernist and Comet) > >Gothmog may be also stronger than Comet. > >Uri Comet is MTD(f)? I haven't noticed it. However, Anmon clearly is. BTW, Cilian looks like it is MTD(f) too, in which case it is the weakest MTD(f) engine that I know of. José C.
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