# MATLAB function help!

1. Oct 16, 2011

### Faux Carnival

Hello everyone, I am fairly new to MATLAB. I have to approximate a root of a given function with Newton-Raphson method.

I have a code that looks like this: (newton.m)

Code (Text):
function [p0,err,k,y] = newton(f,df,p0,delta,epsilon,max1)

%Input     - f is the object function
%            - df is the derivative of f
%            - p0 is the initial approximation to a zero of f
%            - delta is the tolerance for p0
%            - epsilon is the tolerance for the function values y
%            - max1 is the maximum number of iterations
%Output - p0 is the Newton-Raphson approximation to the zero
%            - err is the error estimate for p0
%            - k is the number of iterations
%            - y is the function value f(p0)

%If f and df are defined as M-file functions use the @ notation
% call [p0,err,k,y]=newton(@f,@df,p0,delta,epsilon,max1).
%If f and df are defined as anonymous functions use the
% call  [p0,err,k,y]=newton(f,df,p0,delta,epsilon,max1).

%  NUMERICAL METHODS: Matlab Programs
% (c) 2004 by John H. Mathews and Kurtis D. Fink
%  Complementary Software to accompany the textbook:
%  NUMERICAL METHODS: Using Matlab, Fourth Edition
%  ISBN: 0-13-065248-2
%  Prentice-Hall Pub. Inc.
%  One Lake Street
%  Upper Saddle River, NJ 07458

for k=1:max1
p1=p0-f(p0)/df(p0);
err=abs(p1-p0);
relerr=2*err/(abs(p1)+delta);
p0=p1;
y=f(p0);
if (err<delta)|(relerr<delta)|(abs(y)<epsilon),break,end
end

What do I do now? I really need some help here. Do I need to define f and df first? And how?

Thanks.

2. Oct 16, 2011