NotANumber 2008-07-18 20:00:46 2008-07-18 20:00:46 Definition % this is the default PlanetMath preamble. as your knowledge % of TeX increases, you will probably want to edit this, but % it should be fine as is for beginners. % almost certainly you want these \usepackage{amssymb} \usepackage{amsmath} \usepackage{amsfonts} % used for TeXing text within eps files %\usepackage{psfrag} % need this for including graphics (\includegraphics) %\usepackage{graphicx} % for neatly defining theorems and propositions %\usepackage{amsthm} % making logically defined graphics %\usepackage{xypic} % there are many more packages, add them here as you need them % define commands here In a computer, {\em not a number} (usually abbreviated {\em NaN}) indicates that an arithmetical operation has resulted in a value that is not a number understood (or representable) by the computer. Division by zero is one frequent cause of a result being NaN. Asking for the square root of a negative number is another operation that can result in NaN (unless the computer has been programmed to recognize imaginary numbers). NaN is not a specific value that can be tested for with the usual comparison operators. The programmer is advised to test for NaN with a special function provided by the programming language (such as \verb=isNaN(x)= in JavaScript. Generally, computer algebra systems do not report NaN results even if they do display an error message for a given operation. \begin{thebibliography}{1} \bibitem{df} David Flanagan, {\it JavaScript the Definitive Guide: The Definitive Guide}. New York: O'Reilly (2006): 24 \end{thebibliography}