Index error when using function

I'm getting this error:

Array indices must be positive integers or

logical values.

Error in newton (line 16)

x = x - (f(x))/dx(x);

Answer 1

[James Tursa]

We need to see more of your code to be sure, but you likely have a variable named either f or dx that is shadowing a function of the same name. The solution is to pick a different name for this variable.