HELP need to run Chebyshev code!

I have been trying to run the following code in MATLAB but to no avail. My version is really outdated. R2007b

%%Matlab code for Chebeval
clc
clear all
%all given x
x=linspace(-1,1,101);
%N=5;
N=5;
%chebeval matrix for given N
mat=chebeval(x,N);
%plotting all N=0 to 5
for i=1:N+1
    str{i}=sprintf('N=%d',i-1);
    hold on
    plot(squeeze(mat(i,:)))
end
legend(str)
%function for chebeval
function mat=chebeval(x,N)
syms xx
T0(xx)=1+0*xx;
T1(xx)=xx;
mat(1,1:length(x))=ones(1,length(x));
mat(2,1:length(x))=T1(x);
for i=3:N+1
    
    T2(xx)=2*xx*T1(xx)-T0(xx);
    
    mat(i,1:length(x))=T2(x);
    T0=T1;
    T1=T2;
end
end

When I ran the code from the Editor window, I get the following message:

??? Error: File: ChebevalNUMAssignment1.m Line: 18 Column: 1

Function definitions are not permitted at the prompt or in scripts.

And if paste it and run it from the command window, I get the following message:

??? Undefined function or method 'chebeval' for input arguments of

type 'double'.

So, what should I do? Please help me, I tried so many times and I am new to MATLAB

[Dyuman Joshi]

Do you have the symbolic toolbox?

Also, I would recommend you to first make a function file and then call the function from commond window.

[Beata Dongwi]

I cannot find the symbolic toolbox, perhaps it does not exist in my version.

I will try to follow instructions on how to create a function file and then see what happens.

[Rik]

Your question is not urgent, the reason for that is explained here. I will format your question for you and remove the word urgent.

[Dyuman Joshi]

@Beata Dongwi, even if you follow my instructions, you will get an error, as using syms() function requires symbolic toolbox.

Also, Symbolic toolbox (or any other toolbox for that matter) doesn't come inbuilt with MATLAB. You have to install a toolbox manually.

[Beata Dongwi]

@Dyuman Joshi, I see what the problem is; I am busy installing a newer version now.

Thank you for taking out time to assist me. Very appreciated.

Answer 1

[Bjorn Gustavsson]

Save your chebeval-function in a separate file chebeval.m. Then call that function from your script. For now you can put both script and function in the same working directory.

This way it becomes far easier to reuse the functions you write later on. That way you build up a set of tools which makes your programming incrementally stronger since you start to have tools to solve more complex problems later on, or at least tools that almost solves those problems and you only need to make smaller modifications to develop the new solution.

Once you've taken this step you will at some stage realize that it is preferable to organise your tools/functions in a better way and then you can group similar tools into toolboxes/different directories.

HTH

[Beata Dongwi]

Thank you very much, I will try it right away