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发表于 2019-8-8 13:34:56
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Complex functions[edit]
Basins of attraction for x5 − 1 = 0; darker means more iterations to converge.
Main article: Newton fractal
When dealing with complex functions, Newton's method can be directly applied to find their zeroes.[8] Each zero has a basin of attraction in the complex plane, the set of all starting values that cause the method to converge to that particular zero. These sets can be mapped as in the image shown. For many complex functions, the boundaries of the basins of attraction are fractals.
In some cases there are regions in the complex plane which are not in any of these basins of attraction, meaning the iterates do not converge. For example,[9] if one uses a real initial condition to seek a root of x2 + 1, all subsequent iterates will be real numbers and so the iterations cannot converge to either root, since both roots are non-real. In this case almost all real initial conditions lead to chaotic behavior, while some initial conditions iterate either to infinity or to repeating cycles of any finite length.
Curt McMullen has shown that for any possible purely iterative algorithm similar to Newton's Method, the algorithm will diverge on some open regions of the complex plane when applied to some polynomial of degree 4 or higher. However, McMullen gave a generally convergent algorithm for polynomials of degree 3.[10]
https://en.wikipedia.org/wiki/Newton%27s_method
维基百科上面的这个是什么意思呢? |
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