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Reference.org
Cross-entropy
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<p>In <a href="/facts/Information_theory/qNLH3U5P">information theory</a>, the cross-entropy between two <a href="/facts/Probability_distribution/EpsKKVRu">probability distributions</a> p {\displaystyle p} and q {\displaystyle q} , over the same underlying set of events, measures the average number of <a href="/facts/Bit/S972NSaD">bits</a> needed to identify an event drawn from the set when the coding scheme used for the set is optimized for an estimated probability distribution q {\displaystyle q} , rather than the true distribution p {\displaystyle p} . </p>