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There are two related semantics, if talking of a Fail-Low - inside the search tree or if using aspiration windows at the root.

Inside the Tree

A Fail-low appears at so called All-Nodes inside the alpha-beta algorithm, also called Fail-Low nodes. The score returned is a upper bound on the exact score of the node.

Quote by Bruce Moreland [1]:
A fail-low indicates that this position was not good enough for us. We will not reach this position, because we have some other means of reaching a position that is better. We will not make the move that allowed the opponent to put us in this position.

Root with Aspiration

Another meaning of a Fail-Low, is associated with aspiration windows at the root, where one needs to re-search with wider windows to get the true score rather than an upper bound.

Bruce again:
You can also talk about failing high and failing low from the root position, if you use an aspiration window.

See also

Forum Posts

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External Links


  1. ^ Programming - Glossary - Fail Low, Fail High from Bruce Moreland's Programming Topics Site
  2. ^ Naresh Vempala, Subrata Dasgupta (2007). A Computational Model of the Music of Stevie Ray Vaughan. pdf

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