Author: Vincent Diepeveen
Date: 07:07:27 04/13/03
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On April 13, 2003 at 10:01:48, Omid David Tabibi wrote: >On April 13, 2003 at 07:41:00, Vincent Diepeveen wrote: > >>On April 13, 2003 at 00:14:52, Omid David Tabibi wrote: >> >>may i remind you that many programs use R=3 basically with exception sometimes >>of the nullmove of depthleft == 4. >> >>I'm doing more in qsearch than you do. >> >>Further your verification search is using R=3 too with a bug in the hashtables >>management. Because of that bug which is that you do not store in hashtables >>whether a search result is based upon a verification or not, the worst case >>performance of verification search is R=3. > >One of the reviewers of the article asked several questions regarding the use of >hash tables in conjunction with verified null-move pruning. I told him exactly >what I told you, i.e., the depth stored in the hash table is the depth after >reduction (e.g., if we were in depth 6, have a fail-high report and reduce the >depth to 5, then the final stored depth in the hash table is 5). That might be >too conservative a method, but it guarantees that no hash table bugs (of the >form you mention) are encountered. That is not fixing it at all of course. You need to write to hashtable for *every* position that gets stored whether you did or did not do a verification. Then based upon this bit and whether you already did in the current search a verification, you can decide whether you can give a cutoff or not. So your method does not fix the problem at all. It fixes it for a *few* positions only. >However, I did not explicitly mention it in the article, as I preferred that it >remain as an exercise to the reader (and the reviewer also agreed that it might >be best to leave it to the reader to experiment). The method I used might be too >conservative, and so other programmers might achieve even better results by >using a more aggressive use of hash tables. > >> >>Best regards, >>Vincent >> >>>On April 12, 2003 at 22:45:19, Vincent Diepeveen wrote: >>> >>>>On April 12, 2003 at 13:20:51, Omid David Tabibi wrote: >>>> >>>>>On April 12, 2003 at 10:02:43, Uri Blass wrote: >>>>> >>>>>>On April 12, 2003 at 09:17:31, Omid David Tabibi wrote: >>>>>> >>>>>>>Quite an interesting read Vincent. >>>>>>> >>>>>>>I'm afraid you are investing too much in the parallel speedup though. Any >>>>>>>hardware speedup will be linear (at best) while algorithmic enhancements are >>>>>>>exponential. If you manage to search one ply deeper by an algorithmic >>>>>>>improvement, the gain will be more than any parallel speedup can yield. >>>>>> >>>>>>I agree that the hardware speedup from parallel search will be linear at best >>>>>>but linear improvement is not always less than one ply. >>>>> >>>>>Diep is already parallel. I assume that he will get far less than a 4x speedup >>>>>for his latest work on massive parallelism. Assuming an effective branching >>>>>factor of 4, that speedup will equal one ply. >>>> >>>>b.f. = 2.9 >>> >>>Because you are using standard R=3; but is the search reliable? That bf will not >>>be of much use if it causes Diep to find the correct move two plies later in >>>comparison to its competitors. When was the last time you compared Diep's >>>performance to other engines using test suites? >>> >>>BTW, I can get even a smaller branching factor than yours in no time. I will >>>just use standard R=6 :) >>> >>> >>> >>>> >>>>> >>>>> >>>>>> >>>>>>If the number of processors is big then it can be more than one ply. >>>>>> >>>>>>I believe that it is possible to get a lot more than one ply by pruning and >>>>>>extensions but I decided that I prefer first to improve movei's evaluation and >>>>>>only later to improve movei by better pruning and extensions because evaluation >>>>>>is one of the things that is used in decisions about pruning and extensions. >>>>>> >>>>>>I believe that Movei's main problem in games with programs at similiar strength >>>>>>is in the endgame so I will probably do some improvement in that stage before >>>>>>going back to search. >>>>>> >>>>>>Uri
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