# Differential operator in simple equation

Why the manual solution of this partial derivative operator is not the same as in Mathematica, can someone suggest the code is written right or not ? Here is the code

ClearAll[r, θ, f]
oper = Function[{f, θ}, (Sin[θ]/r Subscript[
DifferentialOperatorPrivateoperator[
DifferentialOperator[]], θ][f[θ]])];
f[θ_] := Cos[θ] Subscript[
DifferentialOperatorPrivateoperator[DifferentialOperator[]], r]
oper[f, θ]


Link of the Package that I am using

PacletInstall["https://github.com/carlwoll/DifferentialOperator/releases/download/0.1/DifferentialOperator-0.0.1.paclet"]

• Hello, welcome to Mathematica.SE. Then: 1. Please show us the code text rather than a screenshot, you may want to read this to learn how to copy the code properly: mathematica.meta.stackexchange.com/q/1584/1871 2. Since you're using the package DifferentialOperator, you should add link to the package in your post, not everybody knows that package. Jul 10, 2021 at 16:46

What you have labeled as a function is itself a differential operator. In general, they are to be applied to a function of both r and θ
op1 = Cos[θ]*D[#, r] &;