How can I prevent the user to use a word (like Hello) in the function?

How can I prevent the user to use a word (like Hello) in the function? the function is a string (numbers and words) so... How can I prevent them to use other words?

thanks!

e.x.:

function x = false_position(f,a,b,kmax,tol)

for i=1:kmax

    x0=a;

    x1=b;

    x2(i)=x0-(x1-x0)/(f(x1)-f(x0))*f(x0);

    if (f(x2(i))>0)

        b=x2(i);

    else a=x2(i);

    end

    fprintf('\n x2=%.4f \n, f(x2)=%.4f',x2 (i), f(x2(i)))

    x=x2(i);

end

for i=1:kmax

    erro(i)=x-x2(i);

end

Answer 1

[Walter Roberson]

You should do that kind of validation before you call false_position.

If the function is a string then your reference to f(x1) is going to be a string access. If you want to evaluate the string given a value, you should be switching to function handles (see str2func()) or you should use feval()

It is not clear that you should be forcing the user to avoid all strings other than the variable name: suppose the user wants to use sin() or other similar operations?

Perhaps you should be looking at try/catch instead.

But if you insist... have a look at symvar()