how does global function work in this code?

Hi, I am kind of beginner in MATLAB and I try to use the following code. It seems I should define p and q but I can not figure out how should I enter p and q to the code

      function [CL,e,psi,r] = ARMA_FULL(theta0, data)
  %function CL=ARMA_FULL(theta0,data)

% define the global vector
global p q;

x=data;

% initial parameter set theta0 is a column vector;
% c is the constant of the general ARMA model;
% ar is the (1*p) vector;
% ma is the (1*q) vector;
if p==0;

      % initial parameters for pure moving average model 
      y=x-mean(x);
      ma=theta0(2:end-1);
      s=theta0(end);
.
.
.

[per isakson]

Try to avoid globals. Don't make it a habit to use them.

Answer 1

[per isakson]

Try

    >> global my_global
    >> my_global= 17
    my_global =
        17
    >> global_demo
        17
    >>

where

    function    global_demo()
       global my_global
       disp( my_global )
    end

Matt Fig says: Globals not good.

Search for "globals evil"! You'll find: Global Variables Are Bad and more