MATLAB: How to find real&imagenery part of complecs symbolic expression

Question

lets say i want to get real &imegenry part of symbolic complex expression . so I wrote this simple code :

clc;clear all;
syms a b 
H=a*i+b
real_H=real(H)

how ever the answer is not correct ,is there and other way ?

Answer 1

syms a b real
%.........^
H=a*i+b;
real_H=real(H)
imag_H=imag(H)

Output:

real_H =
b
imag_H =
a