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In mathematics, specifically differential calculus, the inverse function theorem gives sufficient conditions for a function to be invertible in a neighborhood of a point in its domain. The theorem also gives a formula for the derivative of the inverse function. In multivariable calculus, this theorem can be generalized to any continuously differentiable, vector-valued function whose Jacobian determinant is nonzero at a point in its domain. In this case, the theorem gives a formula for the Jacobian matrix of the inverse. There are also versions of the inverse function theorem for complex holomorphic functions, for differentiable maps between manifolds, for differentiable functions between Banach spaces, and so forth. ==Statement of the theorem== For functions of a single variable, the theorem states that if is a continuously differentiable function with nonzero derivative at the point , then is invertible in a neighborhood of , the inverse is continuously differentiable, and : where notationally the left side refers to the derivative of the inverse function evaluated at its value ''f''(''a''). For functions of more than one variable, the theorem states that if the total derivative of a continuously differentiable function defined from an open set of into is invertible at a point (i.e., the Jacobian determinant of at is non-zero), then is an invertible function near . That is, an inverse function to exists in some neighborhood of . Moreover, the inverse function is also continuously differentiable. In the infinite dimensional case it is required that the Fréchet derivative have a bounded inverse at . Finally, the theorem says that : where denotes matrix inverse and is the Jacobian matrix of the function at the point . This formula can also be derived from the chain rule. The chain rule states that for functions and which have total derivatives at and respectively, : Letting be and be , is the identity function, whose Jacobian matrix is also the identity. In this special case, the formula above can be solved for has a total derivative at . The existence of an inverse function to is equivalent to saying that the system of equations can be solved for in terms of if we restrict and to small enough neighborhoods of and , respectively. 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「inverse function theorem」の詳細全文を読む スポンサード リンク
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