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In mathematics, the Bendixson–Dulac theorem on dynamical systems states that if there exists a function (called the Dulac function) such that the expression : has the same sign () almost everywhere in a simply connected region of the plane, then the plane autonomous system : : has no periodic solutions lying entirely within the region. "Almost everywhere" means everywhere except possibly in a set of measure 0, such as a point or line. The theorem was first established by Swedish mathematician Ivar Bendixson in 1901 and further refined by French mathematician Henri Dulac in 1933 using Green's theorem. ==Proof== Without loss of generality, let there exist a function such that : in simply connected region . Let be a closed trajectory of the plane autonomous system in . Let be the interior of . Then by Green's Theorem, : : But on , and , so the integral evaluates to 0. This is a contradiction, so there can be no such closed trajectory . 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「Bendixson–Dulac theorem」の詳細全文を読む スポンサード リンク
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