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Sidi's generalized secant method is a root-finding algorithm, that is, a numerical method for solving equations of the form . The method was published by Avram Sidi.〔 Sidi, Avram, "Generalization Of The Secant Method For Nonlinear Equations", Applied Mathematics E-notes 8 (2008), 115–123, http://www.math.nthu.edu.tw/~amen/2008/070227-1.pdf 〕 The method is a generalization of the secant method. Like the secant method, it is an iterative method which requires one evaluation of in each iteration and no derivatives of . The method can converge much faster though, with an order which approaches 2 provided that satisfies the regularity conditions described below. == Algorithm == We call the root of , that is, . Sidi's method is an iterative method which generates a sequence of approximations of . Starting with ''k'' + 1 initial approximations , the approximation is calculated in the first iteration, the approximation is calculated in the second iteration, etc. Each iteration takes as input the last ''k'' + 1 approximations and the value of at those approximations. Hence the ''n''th iteration takes as input the approximations and the values . The number ''k'' must be 1 or larger: ''k'' = 1, 2, 3, .... It remains fixed during the execution of the algorithm. In order to obtain the starting approximations one could carry out a few initializing iterations with a lower value of ''k''. The approximation is calculated as follows in the ''n''th iteration. A polynomial of interpolation of degree ''k'' is fitted to the ''k'' + 1 points . With this polynomial, the next approximation of is calculated as with the derivative of at . Having calculated one calculates and the algorithm can continue with the (''n'' + 1)th iteration. Clearly, this method requires the function to be evaluated only once per iteration; it requires no derivatives of . The iterative cycle is stopped if an appropriate stop-criterion is met. Typically the criterion is that the last calculated approximation is close enough to the sought-after root . To execute the algorithm effectively, Sidi's method calculates the interpolating polynomial in its Newton form. 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「Sidi's generalized secant method」の詳細全文を読む スポンサード リンク
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