Author: Robert Hyatt
Date: 14:45:11 12/03/02
Go up one level in this thread
On December 03, 2002 at 15:40:09, Frank Phillips wrote:
>I have failed miserably to implement ETC.
>
>My broad understanding is that you try for a transposition table cutoff for each
>move (successor position) at a node before recursing the search from that node.
>In my implementation the search tree is reduced, but Searcher plays noticeably
>weaker in real games, despite its performance on test suites not deteriorating -
>in fact improving slightly. Below is my pseudo code. Any help appreciated.
>
>Frank
>
>for (each move)
>{
> // MakeMove
> // Check for Draws.
> // Extensions for this move.
> tdepth=depth-1+extension;
> hit=HashRetrieve(pboard,tdepth-1,&tscore,&flag);
I am not sure I understand the above. tdepth has already been decremented by 1.
You are doing it a second time. That would seem to incorrectly order the tree,
and assume a hit because the depth is one ply less than it really should be...
Unless you have your search written in a way different than most, where the
normal hash probe is done right at the top for most of us...
> // UnMakeMove
> if (hit)
> {
> tscore=-tscore;
> if (tscore>=beta && (flag==upper_bound || flag==exact_value))
> return (tscore);
> if (tscore<=alpha && (flag==lower_bound || flag==exact_value)
> return (alpha);
> }
> }
>
>The basic idea is that upper_bound for the successor is the same as lower_bound
>for parent etc.
>And I would call the successor with depth=depth-1+extensions, therefore should
>probe the hash table with that depth.
>exact_value == score is equal to stored value.
>lower_bound == score is at least stored value.
>upper_bound == score is at most stored value.
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