error with functions

Hi i keep tryiing to run this function and it keeps giving me an error

function Xs = BisectionRoot( Fun, a, b, To1Max)
Fa = feval(Fun,a);
Fb = feval(Fun,b);
if Fa*Fb > 0
    disp('Error: The function has the same sign at points a and b.')
else
    n = ceil((log10(b-a) - log10(To1Max))/log10(2));

    for i = 1:n
        Xs = (a + b)/2;

        FXs=feval(Fun,Xs);;

        if FXs == 0

            break
        end

        if F(a)*FXs < 0
            b = Xs;
        else
        a = Xs;

        Fa = FXs;
        end    
    end
end

??? function Xs = BisectionRoot( Fun, a, b, To1Max) | Error: Function definitions are not permitted in this context.

Please help me

Thanks

[Hussein]

The goal of this function is to find the solution of any nonlinear equation by using the bisection method

Answer 1

[Image Analyst]

Most likely you have this futher down in an m-file and the top of the m-file is not another named function, but a simple script. You can't do that. Put the name of your m-file at the top after the word function

function mymfile()
  % Stuff
   secondFunction();
end

function secondFunction()
  % More stuff.
end

[Hussein]

Thanks for the answer, but im kinda new to matlab so i dont exactly understand what you are saying. can you explain me how to write a function then call it ? or please give me a link that explains that.

Thanks

Answer 2

[Walter Roberson]

Store the code in a file named BisectionRoot.m and remove it from where you have it now.

If that still does not work: please check whether you have some tab characters in the file, especially right before the word "function".

[Hussein]

ok i took this function and i saved it as BisectionRoot.m in a script file, now i want to assign values for a, b, and To1Max and i want to assign an equation to Fun , how can i do that ?

[Walter Roberson]

At the command line, you invoke

BisectionRoot(Fun, a, b, To1Max)

where you have defined Fun, a, b, and To1max appropriately.

I think you will find that you do not want to assign an equation to Fun: you want to assign an expression to Fun. If you currently have something of the form f(x)=c then use the expression f(x)-c instead of an equation.

There are a variety of choices as to how you define your function. See the documentation for feval() to see what forms it accepts.