68P01-NotANumber.tex

\documentclass[12pt]{article}
\usepackage{pmmeta}
\pmcanonicalname{NotANumber}
\pmcreated{2013-03-22 18:14:09}
\pmmodified{2013-03-22 18:14:09}
\pmowner{PrimeFan}{13766}
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\pmtitle{not a number}
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\pmauthor{PrimeFan}{13766}
\pmtype{Definition}
\pmcomment{trigger rebuild}
\pmclassification{msc}{68P01}

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\begin{document}
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.

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\bibitem{df} David Flanagan, {\it JavaScript the Definitive Guide: The Definitive Guide}. New York: O'Reilly (2006): 24
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