Differentiating a series in maple

Question

I am trying to get the third derivative of a Laurent series in Maple, while keeping it in series form, but it isn't giving me what I need. Here is the photo of what I am trying to do:

It might look like it cut off, but that's really the end of the problem, the third derivative says it is 0, when really it isn't. It also says it is 0 for the first derivative too.

Answer 1

The diff evaluates derivative of an expression, but your l1 is actually an operator. So you need to either evaluate it in z to make it an expression that diff understands, like

diff(l1(z),z$3);

or, you can invoke the D that can calculate derivatives of operators, like this

D[(1$3)](l1);

Alternative solution would be to define l1 already as an expression:

l1:=5*I/(z-I)^6+5/(z-I)^5+2*exp(3*I)*sum((3^(n-6)*(z-I)^(n-6))/n!,n=0..infinity); diff(l1,z$3);

I am using the classic worksheet notation, but you should get the idea.