problem with fzero in my code

fzero won´t work, anyone knows what may be the problem?

[Hanna Sundling]

This is the error message I get

Answer 1

[Fabio Freschi]

your fun is neither acceppting nor using inputs

You should write the symbolic function like this

fun = @(x)cos(x);
x0 = fzero(fun,0.5);

[Walter Roberson]

your fun is neither acceppting nor using inputs

We do not know that. We see @cosx which is a handle to a function that takes a number of inputs that is not known to us because we do not have the source code for it.

fun = @(x)cos(x);

You can also just use

fun = @cos;

This takes the same number of inputs that cos takes. It is not an error to take the handle of a function and pass that to fzero.

[Hanna Sundling]

I changed my code but it srill won´t work, the same error message comes up and I do not get an answer for fzero

[Walter Roberson]

Mathworks does not define any function named xcos or cosx . What would you expect those functions to calculate if they existed ?

[Fabio Freschi]

@Walter: you are right. I assumed the function was cos(x) from the plot a few lines before. If it is not the case, the OP can clarify what he/she wants to do.

@Hanna: what's wrong in the code I posted. It seems to work on my pc

>> fun = @(x)cos(x);
>> tic; x0 = fzero(fun,0.5); toc
Elapsed time is 0.004853 seconds.

The error you posted is saying that function xcos does not exist. What is the analytic expression of the function you are supplying to fzero? If you want the roots of x*cos(x), you should specify this in the definition of anonymous function, e.g.

fun = @(x)x*cos(x);
% ^     ^ \______/
% |     |    your function
% |     input argument, to be used in the function definition
% handle to the function

[Hanna Sundling]

The task is to find the roots to the function y = cosx in the interval -pi, 2pi.

[Walter Roberson]

THen you would use the code that Fabio showed, but with a number of different starting points to get the various roots.

It is not clear why your comments start talking about xsinx when you want to find roots of cosx

[Hanna Sundling]

I am also going to find how many tangents lines that goes torugh the origin for cosx and that is why I talk abot xsinx in my comments.

[Walter Roberson]

I do not understand what tangent lines through the origin for cosx has to do with xsinx ? Tangent lines to cosx would have to do with sinx not xsinx .

Answer 2

[Ekemini Stephen]

Create a function file and save it to the same dierctory as

function y = f(x)
y = cos(x);
end

Then use this function in the section of your script as

%%
fun = @f; % function
x0 = 0.5; % initial point
ff = fzero(fun,x0);