'Problem' with fzero

Hi, hope you all are well. I am here due to a problem with the function called 'fzero'.

On one hand, I have this file: f.m

function y=f(x)
 y= besselj(1,x);

And on the other hand: exercise.m

D=fzero(@f,[0 10]);
 tam=length(D);
 for i=1:tam
 fprintf(' Possible MAX or MIN: f(%f) \n',D(i))
 end

When I run exercise.m, I get this output:

   Possible MAX or MIN: f(0.000000)

I know where this values should be located...

What am I doing wrong? Thanks in advance. PD: I have to use fzero and besselj(1,x) at [0:10]

Answer 1

[Matt J]

Looks like the code succeded to me. Your function does have a root at x=0.

No idea why you display a message involving MAX and MIN unless you were really trying to minimize/maximize the function. But as its name implies, fzero finds zeros, not max's and min's. You might have been looking to use fminsearch()

[JM]

Thanks for your answer. Due to that I realized I should have used f'(x) instead of f(x). Here it is the fixed code:

x=0:10;
 xx=0:0.01:10; 
y= @(x) besselj(1,x); % F(X)

f= @(x) (besselj(0, x) - besselj(1, x)/x); % F'(X)
 for i=2:10

      D=fzero(f,x(i));

   fprintf(' Possible MAX or MIN: f(%f) \n',D)

   end

It gives you all the possible max's and min's (absolutes and relatives) of F(X) evaluated at [0:10] but at 0 and 10. Thanks again. Regards