Section: Inspection Functions
   y = isset('name')
where name is the name of the variable to test.  This
is functionally equivalent to 
   y = exist('name','var') & ~isempty(name)
It returns a logical 1 if the variable is defined 
in the current workspace, and is not empty, and returns
a 0 otherwise.
isset
--> who
  Variable Name       Type   Flags             Size
--> isset('a')
ans = 
 0 
--> a = [];
--> isset('a')
ans = 
 0 
--> a = 2;
--> isset('a')
ans = 
 1