Question

I am new to Matlab and have difficulty understanding global variables. For example

global x y z

What does global mean? Could you give me an example?

Answer 1

Without global, a declared variable has a limited scope, that is, it cannot be used outside the “part” of matlab where it is declared. This wiki article has a decent discussion of what scope is in a generic sense.

For Example, if you declare a variable inside a function definition, then that variable can only be used inside that function – not in another function. If you define a function at the command line (the so-called “base workspace”) it cannot be used in functions.

global defines a variable in the “global” scope – it can be used anywhere, in any function, etc. Except in limited cases, it is generally a bad idea, since it makes controlling how and when a variable has changed very difficult. You are usually better off returning something from a function, then passing it to another.