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In mathematics, Darboux-Froda's theorem, named after Alexandru Froda, a Romanian mathematician, describes the set of discontinuities of a (monotone) real-valued function of a real variable. Usually, this theorem appears in literature without a name. It was written in A. Froda' thesis in 1929 .〔Alexandru Froda, (Sur la Distribution des Propriétés de Voisinage des Fonctions de Variables Réelles ), These, Harmann, Paris, 3 December 1929〕〔''Alexandru Froda – Collected Papers (Opera Matematica), Vol.1'', Ed. Academ. Romane, 2000〕. As it is acknowledged in the thesis, it is in fact due Jean Gaston Darboux 〔 Jean Gaston Darboux (Mémoire sur les fonctions discontinues ), Annales de l'École Normale supérieure, 2-ème série, t. IV, 1875, Chap VI. 〕 ==Definitions== #Consider a function of real variable with real values defined in a neighborhood of a point and the function is discontinuous at the point on the real axis . We will call a removable discontinuity or a jump discontinuity a discontinuity of the first kind.〔Walter Rudin, ''Principles of Mathematical Analysis'', McGraw-Hill 1964, (Def. 4.26, pp. 81–82)〕 #Denote and . Then if and are finite we will call the difference the jump〔M. Nicolescu, N. Dinculeanu, S. Marcus, ''Mathematical Anlaysis'' (Bucharest 1971), Vol.1, Pg.213, (Romanian )〕 of f at . If the function is continuous at then the jump at is zero. Moreover, if is not continuous at , the jump can be zero at if . 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Froda's theorem」の詳細全文を読む スポンサード リンク
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