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I.3 Introduction to the theory of convex conjugated function
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Epigraph E : set Epigraph,is the set
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lower semicontinuous Assume that E is a topological space. Define is called lower semicontinuous (l.s.c) at x if
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i.e. for any there is a neighborhood N of x such that f is l.s.c on E if f is l.s.c at each point of E
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Exercise is l.s.c on E if and only if is open is closed
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is l.s.c on E if and only if is closed in E x R
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is l.s.c on E if and only if is closed
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are l.s.c then so is Ifand
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is l.s.c t h e n t h e u p p e r e n v e l o p e o f If is a family of l.s.c functions on E i.e. the functiondefinded by is l.s.c
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is attained If E is compact and is l.s.c on E,then i.e.
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Convex is convex if D e f Suppose E is a vector space (real)
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is convex if and only if is convex in E x R
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is a convex function then is convex. If forthe set Converse statement is not true in genernal see next page
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counter example
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are convex then so is Ifand
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is convex t h e n t h e u p p e r e n v e l o p e o f If is a family of convex functions on E
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Conjugated function such that G i v e n Assume that E is a real n.v.s D e f i n e t h e c o n j u g a t e d f u n c t i o n o f b y
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proposition 1-9 then i s c o n v e x, l. s. c Suppose
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Def
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Theorem I.10 (Fenchel-Moreau) then i s c o n v e x, l. s. c Suppose
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Example
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Lemma I.4 then i s c o n v e x, Let then IntC is convex If
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Theorem I.11 are convex and suppose that a n d such that Suppose there is and is continuous at see next page
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Observe usually appears for constrain (1) (2) see next page
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The proof of Thm I.11 see next page
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Example
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Exercise
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Example Let be nonempty, close and convex. Put
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Let
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