Changes

a measure of the number of choices ([[Legal Move|legal moves]]) a player has in a given position. It is often used as a term in the [[Evaluation Function|evaluation function ]] of chess programs. It is based on the idea that the more choices you have at your disposal, the stronger your position. A study by [[Eliot Slater]] of 350 tournament games in which the material balance was still even after the 20th move showed a definite correlation between a player's mobility and the number of games won <ref>[[Eliot Slater]] ('''1950'''). ''[http://www.eliotslater.org/index.php/chess/147-statistics-for-the-chess-computer-and-the-factor-of-mobility Statistics for the Chess Computer and the Factor of Mobility]''. Proceedings of the Symposium on Information Theory, London. Reprinted ('''1988''') in [[Computer Chess Compendium]], pp. 113-117. Including the [http://www.eliotslater.org/index.php/chess/159-discussion-on-the-above-paper-alan-turing-et-al-1950 transcript of a discussion] with [[Alan Turing]] and [[Jack Good]]</ref> .

[[Freedom]] and [[Papa]] both use [[Mobility|mobility]] as their primary term in their [[Evaluation functionFunction|evaluation functions]]. As with [[Awit|Wita]], both use the ratio of computer's moves / opponent moves. Papa and Wita also multiply by the ratio of the [[Square Control|squares controlled]] and Papa goes one step further and takes the [https://en.wikipedia.org/wiki/Logarithm logarithm] of this product to form the "[[Papa#Entropy|entropy]]" of the position. The true merit of this entropy over the product ratio was not made clear, but it does ensure that in extreme situations the evaluation remains more closely bounded.