MATLAB: Undefined function ‘eval’ for input arguments of type ‘double’.

Question

When using the code below:

function [Df]=difc(f,u,h)
syms x
x=u+h; lp=eval(f);
x=u-h; ll=eval(f);
Df=(lp-ll)/(2*h);
end

, the same error keeps appearing ''Undefined function 'eval' for input arguments of type 'double'.''

I would like to know what´s the problem and what can I do to solve it, in order to have a working code.

Thankyou very much

Answer 1

You are getting that error because you are trying to evaluate a double. A double is just a double - there is nothing there to evaluate.

What are you expecting the 'eval' function to do?