Author: rasjid chan
Date: 04:38:34 04/06/04
Go up one level in this thread
On April 06, 2004 at 03:07:31, Gerd Isenberg wrote: >On April 05, 2004 at 19:03:52, rasjid chan wrote: > >>On April 05, 2004 at 16:13:15, Gerd Isenberg wrote: >> >>I may need to think a little more as the replies seem to indicate >>more to hashing than I know. >> >>I hope you can clarify on this so that I may clear any misunderstanding >>once and for all :- >>"Replacement scheme is a big issue here" >>1) Do you mean generally in chess programming,replacement scheme is >> a big issue - meaning there are many ways to do hashing and each tries >> to find the best way to implement hash tables. > >Yes, i mean chess programming. Other applications may have similar issues of >course. > > >> ie also there is >> no STANDARD WAY TO IMPLEMENT HASH TRANSPOSITION TABLE. > >With replacement, there are several standards schemes, like replace allways, >depth prefered, expense (number of saved nodes) prefered, multiple slots per >hashkey and to replace the slot with the lowest "worth". > >I use a two table approach, a big one with eight consecutive slots, shared by >several hashkeys and replace the lowest "valuable" entry - and a smaller, faster >one (a few K-entries only) with replace allways scheme. The huge one is >restricted to full search, where the smaller is used everywhere. With multiple >slots per hashkey one may reserve one slot as an always replacement slot >and n-1 slots as prefered "value" replace slots. > >So there are a lot of ways to implement and combine hashing schemes in chess, >specially how to consider the "worth" of an entry. One may count and store the >number of hits per entry and prefere entries with frequent hits over entries >with seldom hits... > >You may put "refutation" information inside the hash table. Each time a root >move is done, you may have a PV (first or best move) or a refutation line, >backed up in a triangular matrix. One may traverse (making moves) this line at >the root and tag the traversed nodes as a kind of "PV" move (the most left path >under one root leaf). Such entries are probably more worth than others and >require a considerable higher depth to get overwritten. Of course with same >depth one should prefere exact score over lower and higher bound values. And >lower bounds values are probably more valuable than upper bounds without any >best move... > >>2) Or are you refering to the specific case in my post. > >What specific case? > >> >>I use the simplest replacement scheme, whether a node is fresh or higher >>/equal depth, maybe some etc... and I have everything in one TT, >>full search, qsearch, null-move and they seem to be working ok. > >Fine, you may try a lot and play around with several replacement schemes to look >what is favorite for your program. And yes, hashing is a complicated affair, >minor changes may have huge influence on the search... > >Cheers, >Gerd > >> >>Best Regards >>Rasjid >> >> >> ><snip> Many Thanks. Some part of your post are on very a very "advanced" technical level which I am certain I won't need for some time, but when it's time and needed they will remind me where to look. So now it is generally correct hashing can be complicated. Best Regards Rasjid
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