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Subject: Selective deepening and Hashtables

Author: Inmann Werner

Date: 06:24:00 06/30/98


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






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