Author: Uri Blass
Date: 23:41:40 01/14/04
Go up one level in this thread
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
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