ISFIELD ISFIELD Test for Existence of a Structure Field

Usage

Given a structure array, tests to see if that structure
array contains a field with the given name.  The syntax
for its use is

  y = isfield(x,field)

and returns a logical 1 if x has a field with the 
name field and a logical 0 if not.  It also returns
a logical 0 if the argument x is not a structure array.
