\documentclass[twocolumn,a4paper]{article}
\usepackage{graphicx}
\begin{document}
\title{$\Gamma$-function}
\author{from Wikipedia}
\maketitle

\begin{abstract}
In mathematics, the gamma function (represented by $\Gamma$, the capital letter
gamma from the Greek alphabet) is one commonly used extension of the
factorial function to complex numbers.
\end{abstract}

\section{Introduction}
The gamma function is defined for all complex numbers except the
non-positive integers. For any positive integer $n$,
	\begin{equation}
\Gamma(n)=(n-1)! \;.
	\end{equation}
Derived by Daniel Bernoulli, for complex numbers with a positive real part, the gamma function is defined via a convergent improper integral:
	\begin{equation}\label{eq-def}
\Gamma(z) = \int_0^\infty x^{z-1} e^{-x}\,dx, \ \qquad \Re(z) > 0\ .
	\end{equation}

Here is a reference to equation~(\ref{eq-def}).

The gamma-function is illustrated on Figure~\ref{fig-gamma} using
\em{gnuplot} with \em{cairolatex} terminal.

\begin{figure}[b]
\input{fig-gamma}
\caption{Illustration of the gamma-function with gnuplot and cairolatex
terminal.}
\label{fig-gamma}
\end{figure}

\begin{figure}[b]
\includegraphics{fig-gamma-pyx.pdf}
\caption{Illustration of the gamma-function with pyxplot pdf terminal.}
\label{fig-gamma-pyx}
\end{figure}


\end{document}
