PositiveSemidefinite2 2008-01-04 22:43:16 2008-01-04 22:43:16 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 A rational function $f\in\mathbb{R}(X_1,\ldots,X_n)$ is \emph{positive semidefinite} if $f$ is nonnegative whenever it is defined.