\section{ISNAN Test for Not-a-Numbers}

\subsection{Usage}

Returns true for entries of an array that are NaN's (i.e.,
Not-a-Numbers).  The usage is
\begin{verbatim}
   y = isnan(x)
\end{verbatim}
The result is a logical array of the same size as \verb|x|,
which is true if \verb|x| is not-a-number, and false otherwise.
Note that for \verb|complex| or \verb|dcomplex| data types that
the result is true if either the real or imaginary parts
are NaNs.
\subsection{Example}

Suppose we have an array of floats with one element that
is \verb|nan|:
\begin{verbatim}
--> a = [1.2 3.4 nan 5]
a = 
  <double>  - size: [1 4]
 
Columns 1 to 4
   1.2    3.4    nan    5.0  
--> isnan(a)
ans = 
  <logical>  - size: [1 4]
 
Columns 1 to 4
 0  0  1  0  

\end{verbatim}
