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v2007.09.13 - Convex Optimization

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Chapter 3Geometry of convex functionsThe link between convex sets and convex functions is via theepigraph: A function is convex if and only if its epigraph is aconvex set.−Stephen Boyd & Lieven Vandenberghe [46,3.1.7]We limit our treatment of multidimensional functions 3.1 to finite-dimensionalEuclidean space. Then the icon for the one-dimensional (real)convex function is bowl-shaped (Figure 59), whereas the concave icon is theinverted bowl; respectively characterized by a unique global minimum andmaximum whose existence is assumed. Because of this simple relationship,usage of the term convexity is often implicitly inclusive of concavity in theliterature. Despite the iconic imagery, the reader is reminded that the setof all convex, concave, quasiconvex, and quasiconcave functions contains themonotonic functions [150] [157,2.3.5]; e.g., [46,3.6, exer.3.46].3.1 vector- or matrix-valued functions including the real functions. Appendix D, with itstables of first- and second-order gradients, is the practical adjunct to this chapter.2001 Jon Dattorro. CO&EDG version 2007.09.13. All rights reserved.Citation: Jon Dattorro, <strong>Convex</strong> <strong>Optimization</strong> & Euclidean Distance Geometry,Meboo Publishing USA, 2005.183

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