php man page for is_nan

IS_NAN(3)								 1								 IS_NAN(3)

is_nan - Finds whether a value is not a number

SYNOPSIS
       bool is_nan (float  $val)

DESCRIPTION
	Checks whether $val is 'not a number', like the result of acos(1.01).

PARAMETERS
	      o $val
		- The value to check

RETURN VALUES
	Returns TRUE if $val is 'not a number', else FALSE.

EXAMPLES
       Example #1

	      is_nan(3) example

	      <?php
	      // Invalid calculation, will return a
	      // NaN value
	      $nan = acos(8);

	      var_dump($nan, is_nan($nan));
	      ?>

	      The above example will output:

	      float(NAN)
	      bool(true)

SEE ALSO
       is_finite(3), is_infinite(3).

PHP Documentation Group 														 IS_NAN(3)