diff function for "Differentiate symbolic expression or function" vs "Differences and Approximate Derivatives"

I am trying to use diff as the first option but it keeps doing the second. How can I make it differentiate instead of doing the differences one? They both have the same function caller.

Answer 1

[Ameer Hamza]

If the input is a symbolic expression, it will differentiate it. If the input is a numeric matrix, it will calculate the difference. For example,

syms x
d = diff(sin(x))
d =
  cos(x)

also

diff([1 2 3])
ans =
   1     1

So it depends on the input type, that how the diff() function will behave.