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Subject: Programmers: ETC

Author: Peter McKenzie

Date: 12:23:15 02/13/03


Just wondering how many programs are using the Enhanced Tranposition Cutoffs
algorithm, or if people have tried it and had trouble with it.  I think I'll
have a go at implementing it shortly.

For those interested, here is the basic idea:

When searching a position, the first thing done is a search of the hash table.
Assuming this doesn't result in a fail high, we then try ETC.

For each possible move, do a make move and check the hash table.  If the hash
table indicates that the side to move would fail low (it must have sufficient
draft of course) then you can fail high in the original position.

I guess the tricky thing is making sure that alpha and beta are handled
correctly.

There are possible tricks to make it work better:
- only do ETC when remaining depth is reasonably high
- have a special fast makemove which updates the hash key only
- even if ETC doesn't provide a cutoff, perhaps it can help move ordering

Any tips are most welcome.

thats all,
Peter



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