ISNAN ISNAN Test for Not-a-Numbers

Usage

Returns true for entries of an array that are NaN's (i.e.,
Not-a-Numbers).  The usage is

   y = isnan(x)

The result is a logical array of the same size as x,
which is true if x is not-a-number, and false otherwise.
Note that for complex or dcomplex data types that
the result is true if either the real or imaginary parts
are NaNs.