\section{ISFIELD Test for Existence of a Structure Field}

\subsection{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
\begin{verbatim}
  y = isfield(x,field)
\end{verbatim}
and returns a logical \verb|1| if \verb|x| has a field with the 
name \verb|field| and a logical \verb|0| if not.  It also returns
a logical \verb|0| if the argument \verb|x| is not a structure array.
\subsection{Example}

Here we define a simple struct, and then test for some 
fields
\begin{verbatim}
--> a.foo = 32
a = 
  <structure array> - size: [1 1]
    foo: [32]
--> a.goo = 64
a = 
  <structure array> - size: [1 1]
    foo: [32]
    goo: [64]
--> isfield(a,'goo')
ans = 
  <logical>  - size: [1 1]
 1  
--> isfield(a,'got')
ans = 
  <logical>  - size: [1 1]
 0  
--> isfield(pi,'round')
ans = 
  <logical>  - size: [1 1]
 0  

\end{verbatim}
