Author: Charles Roberson
Date: 07:38:41 04/07/05
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You misunderstand. Modern programs are not truely "full width" searchers.
They prune 90% to 95% of the positions. Where the branchfactor is near 40.
The effective branch factor is near 3. The search is a directed search
thus it only evaluates what it needs to.
Once the PV is established, move ordering is used to create fast cutoffs.
Thus, modern programs only search what they need to (within their
understanding) and evaluate only what they search. Now, there is Lazy
Evaluation which prunes some of the evaluation effort in very unbalanced
positions. Thus, current practice is not to do full evaluation on all
positions evaluated.
The way your statement goes (if I understand it), you assume a full width
search is done. That is not truely the case.
Today, the phrase "full width" means that it is provable that this search
produces the same results as a full width search without being a true full
width search. That is where the statements of "safe pruning" and "unsafe
prunning" come in.
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