Author: Robert Hyatt
Date: 13:22:32 06/30/98
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On June 30, 1998 at 09:24:00, Inmann Werner wrote: >Selective deepening and Hashtables > >Problem: >In alpha.beta , there is a variable distance (distance to the horizon) , which >is decreased each call of >Alpha-beta. >If you have, lets say for example, a check, you want to deepen the search. I do >this by increasing >The variable distance. > >If you insert the position in the hashtable, you write the variable distance in >the hash table. >(I do so). >I only take hashtable entrys, where the distance in it is more than the actual >distance. (why not?) > >If a search the move one ply deeper the next time (iterative deepening) and >look at the hash table, the Position has a very good value of the variable >distance because of the selective deepenings made in the Last search. Because >the program knows nothing about the actual selective deepenings, which will come >In the search it is satisfied and takes the hash entry. > >And thats the problem. The search nearly never looks really deeper in this move, >because it takes it always fFrom the hash table until my search is deeper then >all previous extensions. > >Is my problem-analysis ok? Have I forgot something important or stupid? > >If not, what can I do? > >Should I write the "distance - number of extensions" when I write to the Hash >table? What follows then out of this!? > > >Werner This should not happen. When you enter ply "P", with a remaining depth of "X", you do a lookup right there. If you can't cutoff, you search all the moves at ply "P", and when you finish, you store the result with a depth of "X" still. And then there is no way your scenario can happen. You don't pay any attention to the depth *after* you play a move at this ply, because when you do the probe the next search, you would be comparing the wrong draft to the current depth remaining...
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