Chapter 1: Problem 6
Sketch a function \(f\) and initial guess for which Newton's Method diverges.
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Chapter 1: Problem 6
Sketch a function \(f\) and initial guess for which Newton's Method diverges.
These are the key concepts you need to understand to accurately answer the question.
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If the Secant Method converges to \(r, f^{\prime}(r) \neq 0\), and \(f^{\prime \prime}(r) \neq 0\), then the approximate error relationship \(e_{i+1} \approx\left|f^{\prime \prime}(r) /\left(2 f^{\prime}(r)\right)\right| e_{i} e_{i-1}\) can be shown to hold. Prove that if in addition \(\lim _{i \rightarrow \infty} e_{i+1} / e_{i}^{\alpha}\) exists and is nonzero for some \(\alpha>0\), then \(\alpha=(1+\sqrt{5}) / 2\) and \(e_{i+1} \approx\left|\left(f^{\prime \prime}(r) / 2 f^{\prime}(r)\right)\right|^{\alpha-1} e_{i}^{\alpha} .\)
Consider the Fixed-Point Iteration \(x \rightarrow g(x)=x^{2}-0.24\). (a) Do you expect Fixed-Point Iteration to calculate the root \(-0.2\), say, to 10 or to correct decimal places, faster or slower than the Bisection Method? (b) Find the other fixed point. Will FPI converge to it?
Apply two steps of the Secant Method to the following equations with initial guesses \(x_{0}=1\) and \(x_{1}=2\). (a) \(x^{3}=2 x+2\) (b) \(e^{x}+x=7\) (c) \(e^{x}+\sin x=4\)
Assume that \(g\) is a continuously differentiable function and that the Fixed- Point Iteration \(g(x)\) has exactly three fixed points, \(-3,1\), and 2. Assume that \(g^{\prime}(-3)=2.4\) and that FPI started sufficiently near the fixed point 2 converges to 2 . Find \(g^{\prime}(1)\).
Find the forward and backward error for the following functions, where the root is \(3 / 4\) and the approximate root is \(x_{a}=0.74\) : (a) \(f(x)=4 x-3\) (b) \(f(x)=(4 x-3)^{2}\) (c) \(f(x)=(4 x-3)^{3}\) (d) \(f(x)=(4 x-3)^{1 / 3}\)
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