Author: Dann Corbit
Date: 10:35:23 01/15/04
Go up one level in this thread
On January 15, 2004 at 09:50:18, José Carlos wrote: >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. It [Cilian] is also one of the first implementations. Here's a fresh compile: ftp://cap.connx.com/chess-engines/new-approach/CILIAN.exe
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.