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# MEI C3 Maths Coursework- Newton Raphson Failure watch

1. Does it still count as a failure if 0 is the closest integer to both roots, but newton-raphson can only find one root for input 0? It still finds the other root, but not with the input of the closest integer to the root.

For example, would this equation count as a failure?
x^3+7x^2-0.231x-0.231
2. (Original post by couruthim)
Does it still count as a failure if 0 is the closest integer to both roots, but newton-raphson can only find one root for input 0? It still finds the other root, but not with the input of the closest integer to the root.

For example, would this equation count as a failure?
x^3+7x^2-0.231x-0.231
I don't quote understand the question. Can you rephrase?

0 is the closest integer to two of the roots and -7, to the other.
3. (Original post by couruthim)
Does it still count as a failure if 0 is the closest integer to both roots, but newton-raphson can only find one root for input 0? It still finds the other root, but not with the input of the closest integer to the root.
Newton Raphson will converge to one root depending on which basin of attraction your initial guess in. What do you expect? For it to converge to one root the first time and then do the exact same thing and have it converge to the other root? I'm not understanding.

For example, would this equation count as a failure?
x^3+7x^2-0.231x-0.231
That's not an equation.
4. (Original post by Zacken)
Newton Raphson will converge to one root depending on which basin of attraction your initial guess in. What do you expect? For it to converge to one root the first time and then do the exact same thing and have it converge to the other root? I'm not understanding.

That's not an equation.
Sorry, I meant to write = 0 on the end

I've clarified my doubts regarding the question, but one general question:
Does anyone have examples of equations where Newton Raphson might fail other than where gradient = 0?
5. (Original post by couruthim)
Sorry, I meant to write = 0 on the end

I've clarified my doubts regarding the question, but one general question:
Does anyone have examples of equations where Newton Raphson might fail other than where gradient = 0?
Is this useful: https://www.quora.com/When-does-Newton-Raphson-fail ?

This has some nice visualisations: http://www3.ul.ie/~mlc/support/CompM...fficulties.pdf

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