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I want list of failure cases for Newton-Raphson method. If possible please provide flow chart for Newton-Raphson method.

abcdmath
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  • Where the derivative is $0$ or undefined is an obvious case – Rhys Hughes May 15 '18 at 09:11
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    Welcome to MSE. It will be more likely that you will get an answer if you show us that you made an effort. – José Carlos Santos May 15 '18 at 09:12
  • i know few, i asked as it would be great if there will be a list of all possible failure cases at one place – abcdmath May 15 '18 at 09:29
  • If the function is too fast-changing / "noisy" and our derivative estimate does not take this noise into account. – mathreadler May 15 '18 at 09:33
  • With initial approximation $x_0$ to solution $x,$ if the derivative $ f' $ of the function $f$ vanishes or takes values arbitrarily close to $0$ on the open interval between $x_0$ and $ x$ then for some $n$ we may have $f'(x_n)=0$ for some $n$ or it may be that $f(x_n)\ne 0$ and that $f'(x_n) $ is so close to $0$ that $x_{n+1}$ can be "almost anywhere". – DanielWainfleet May 15 '18 at 13:23
  • A flagger suggested that duplicate. While the answers to the dupe target don't get to the bottom of it, some of them do explain what can go wrong. Closing this as a dupe as a way of better organizing the site. Do follow up the link to a third thread from the dupe target. More interesting ways for Newton-Rhapson to fail. – Jyrki Lahtonen May 16 '18 at 05:54

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The Newton-Raphson Method is:

$$x_{n+1}=x_n-\frac{f(x_n)}{f'(x_n)}$$

Since a fraction $\frac ab$ is undefined when $b=0$ or undefined, in this case that constiutes an equation $f(x)$ whose derivate cannot be found or is $0$.

Rhys Hughes
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