In mathematical analysis, the Alexandrov theorem, named after Aleksandr Danilovich Aleksandrov, states that if U is an open subset of Rn and f : U → Rm is a convex function, then f has a second derivative almost everywhere.
In this context, having a second derivative at a point means having a second-order Taylor expansion at that point with a local error smaller than any quadratic.
The result is closely related to Rademacher's theorem.
- Niculescu, Constantin P.; Persson, Lars-Erik (2005). Convex Functions and their Applications: A Contemporary Approach. Springer-Verlag. p. 172. ISBN 0-387-24300-3. Zbl 1100.26002.
- Villani, Cédric (2008). Optimal Transport: Old and New. Grundlehren Der Mathematischen Wissenschaften. 338. Springer-Verlag. p. 402. ISBN 3-540-71049-3. Zbl 1156.53003.
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