The command defined determines whether the variable M is defined in MATLAB. By default, when no attribute parameter is specified, the defined command checks whether a variable named M exists in the MATLAB environment.

If the command contains the optional parameter 'function', then defined returns a value of 'true' only if a function named  is defined in the MATLAB environment. The option 'globalvar' returns 'true' if the variable M is defined in the MATLAB environment and it is a global variable.

To set a global variable in MATLAB, define the variable as a global by using Matlab[setvar], with the optional parameter 'globalvar' as in the calling sequence Matlab[setvar]("M", value, 'globalvar'). Variables must be declared as global to work with functions that use global variables of the same name.

The defined command establishes whether M exists in the MATLAB session.  Executing the defined command returns either 'true' or 'false'.