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Subject: Re: MTD(f)

Author: rasjid chan

Date: 00:02:05 06/18/05

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"I see no reason to ever fail hard. I don't even see how fail-soft is more
bug-prone"

I think some(many?) don't use fail-soft because there is almost always
too long a "todo" list with high priority.

If I am not wrong, after we get through with how to implement it correctly, it
"should be" bug free. Maybe the method may be summarize in just a few principles
to stick to, basically :-
1) when returning from any search(), return a return_type of ex/ub/lb/rep3
2) when we store  a best-score for exact, fail-low or fail-high,we
   apply revere_type() which only reveresd the type of ub/lb.
3) when we fail-high and the "best_type" is ex and if the move happen
to be the last move left(more often in QS), we upgrade the return_type from the
usual lb for fail-high to ex.

This may be "about all" and maybe some other finer details that most
chess programers should easily know.

The problem is I have not monitored the "softness" of my fail soft.
If fail-soft is really soft to a fair degree, why should anyone "fall-hard".
When we store scores to HT, we may have a greater LB or lesser UB which
is always better.

Regards
Rasjid



















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