# Matlab Secant Method

Recall that Newton's Method is an iterative way of approximating a zero of a function $$f$$. The idea is that, given a starting guess $$x_0$$ and an error tolerance $$\tau$$, we compute new estimates of the zero of $$f$$ using the formula $x_{n+1} = x_n-f(x_n)/f'(x_n)$ for $$n=0,1,\ldots$$ We use this iteration until $$\vert x_n-x_{n-1}\vert\lt\tau$$ or until we give up trying. Unfortunately, we do not know how to use Matlab to compute the derivative of $$f$$ (it can, we just have not done it). Instead, we can choose some small number $$h$$ and use the approximation $f'(x_n) \approx \frac{f(x_n)-f(x_n-h)}{h}$ instead of $$f'$$. If we use successive estimates of the root, then the formula becomes $x_{n+1}=\frac{x_{n-1}f(x_n)-x_nf(x_{n-1})}{f(x_n)-f(x_{n-1})}.$ This is called the secant rule. Write a Matlab function secant(f,init_guess,tolerance) that finds the zero of a function using this secant formulation.

The "final exam" for this course will take place at 8:00 AM on Tuesday, 12 December. This will be an ordinary 50 minute test. It will be comprehensive, but weighted toward the latter half of the semester. As always, paper notes will be permitted, but no electronic devices will be allowed. A sample exam is available.

A Solution example is available for the quiz. The solution to Test 1 is still available too.

The ultimate assignment is posted.

Department of Mathematics, PO Box 643113, Neill Hall 103, Washington State University, Pullman WA 99164-3113, 509-335-3926, Contact Us