Author: Robert Hyatt
Date: 19:30:40 10/13/99
Go up one level in this thread
On October 13, 1999 at 22:00:32, Ratko V Tomic wrote: >>>Even the 18 plies in complex middle game (which may be 2-3 years off) still >>>hinge on the same old simple-minded evaluation of the terminal nodes. >> >>You think DB uses 'the same old simple-minded evaluation'? >> > >I would say the terminal node evaluation (excluding the table-base lookup, of >course) in any program is simple-minded comapared to human judgment. By itself, >this evaluation makes it roughly equivalent to one ply "search" setting, which >should lose to just about any chess player. > you ought to play a program with a 1 ply depth limit, which is basically relying totally on that 'evaluation' you mentioned. I think you'll find that the evaluation is far stronger than just a "1 ply search with no evaluation at all". Many programs have a fair amount of knowledge in them. Some probably know more about some parts of the game than all but GM-type players... >Regarding DB vs other chess programmers, I would think that the best commercial >programs use more sophisticated algorithms than DB. That's human nature -- if >hardware will do 200 Mnps without programmer breaking a sweat, the drive to >conceive something new here to squeeze an extra 10 or 50 Mnps won't be nearly as >strong as if you're using 40 knps micro (as in case of Hiarcs on a 400 Mhz >Celeron). Thus the micro chess programmers have to think much harder to produce >the highest quality evaluation functions, while DB programmers can stuff almost >anything that comes to mind, and very likely don't put nearly as much thought >and creativity into it as the micro guys do. As the saying goes, the necessity >is mother of invention. > > >>>If I (a mere 2100 player over a decade ago) can get Fritz 5.32 etc to just >>>shuffle rooks on the back rank with no clue what to do next, >> >>But if you let Fritz search more ply (15, 20, ...ply), it will eventually find >>something better to do than shuffle rooks. Other programs may not have this >>problem at all. >> > >Depends on type of positions. In some positions there is virtually no (humanly) >non-obvious tactics hinging critically on a move choice 20-30 plies earlier. >Whether at ply 20 Fritz will find something (that's still at least 5 years from >the current full depths, though), depends on what it is looking for. It may find >how to gain an attack on one extra square, which may mean nothing, or may even >make things worse 15 plies later. > >While deeper is on average better, if it were always better, the same program >running on a two times as slow machine would always lose to the program on the >faster machine. That's not true, though. If, say, the factor 2 in speed brings >70 ELO points, the (W-L)/(W+L)=70/400=0.175, giving then W/L= 1.42 or giving >percentage wins about 60% for the faster version. So quite a good deal of time >the shallower search gave _ultimately_ better moves. > >Now if one were to develop more systematic theory (for human use) on what kind >of positions have such property and strategic methods to go along to produce >such positions, that could negate much of the computer depth gain. There are >also artificially constructed (for this purpose only) games where deeper search >produces mostly worse moves (than e.g. a random pick of moves). > > >The reason for all these counterintuitive phenomena is that minimax as used in >chess is not really picking the best among the exact values of the nodes but the >best of the guessed values (guessed by some rules of thumb, which are nowhere >near 100% valid). The programs also have no idea how much error is involved in >these estimates but treat them as if they were true values to be minimaxed. A >program will, without a second thought, go for massive complications, showing >near term win of additional material, even when their current material is >already winning for any half good player. A rational human player will convert >the advantage to a whole point in the most safe, least double edged way. > > >>> You don't need the best move to win, just a good enough move (chess >> programmers don't seem to know this, as yet). >> >>So do you want the chess programs to say "Ok, I have 3 choices for moves, and >>all look like they're 'good enough'. I think I'll choose the one that I think >>is the worst of the 3, because it's still 'good enough'." ? >> > >No, I didn't say that. What I said is that if, say, a program sees a 12 ply sure >win of a piece, with otherwise quiet and "normal" position, then there is no >need to pursue alternatives to its choices which at ply 14 might gain a piece >plus pawn. It should pursue deeper only the branch which it already discovered >winning a piece, to verify the gain isn't poisoned, otherwise it should be happy >to have found one very likely way to the whole point. Programs seem to calculate >as if your score will go up point and half if you can win in 30 moves instead of >45 moves. As of now, it won't, thus no need to waste its time (which may be >needed later in the game if the oponent tries something desperate) as if it >will. > >(Of course, being happy with "good enough" would have to be turned off when >solving test suites, otherwise they might not find the solution.) > > >>A different move almost always is better if it's found at greater depth. > >If that were so, the same program on 400 Mhz PII would win "almost always" to >the program on 200 Mhz Pentium, and that's not the case at all, while in fact >the faster one will win only about 60% of games. > >>> I'll >>use your example: Say at depth 10, the program sees that it can do Qxb2, >>winning a pawn. If it searches to depth 11, say, it may see that it's getting >>attacked, since it doesn't have its queen to defend. So it picks a different >>move, that doesn't win the b2 pawn, but does prevent your attack. >> >>Is this not a better move, found because of greater depth? >> > >But at ply 1-9 it may have not seen a win of the pawn at all, so it wouldn't >have gotten drawn into the queenside pawn hunting at all. As suggested earlier, >it all depends on types of positions, and while the typical present-day human >style positions may be vulnerable to deeper search in a statistically >significant number of cases, I have no doubnt that a different style, from >openings to strategic guidlines, exist which would shift the probabilities >making the extra depth, while not necessarily do more harm, but at least do not >much good for the typical alpha-beta searcher.
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