Error implementing Newton's Method

Tried implementing Newton's Method in MATLAB, but receiving this error regarding indexing. Not sure what this means or how to fix it.

Answer 1

[Walter Roberson]

syms x
f = @(x) x^3 - 2*x^2 - 5;
df = diff(f,x)

df = 

class(df)

ans = 'sym'

Notice that the class of df is sym. df is a symbolic scalar. Attempting to invoke df(po) is an attempt to index the symbolic scalar df at the location indicated by po

What you need is

df = matlabFunction( diff(f, x) )