[Tex/LaTex] No comma between multiple authors in bibliography

bibtexnatbib

I am trying to write a paper and at the bibliography I have several titles which contain multiple authors. I want a comma to appear between them, but even if in the bib file I write the authors with comma between them, in the pdf the comma does not appear. I am trying to do this using natbib. A friend sent me a paper which uses natbib and when I compiled it the comma appeared, but the same code does not work in my paper.

This is my paper:

\documentclass[a4paper,10pt]{report}
\usepackage[round]{natbib}
\usepackage[utf8x]{inputenc}
\usepackage{hyperref}

\title{Title}
\author{Author}

\date{}

\begin{document}
\maketitle
\begin{abstract}
  Abstract
\end{abstract}

\section{Introduction}
\cite{williamson}

\bibliographystyle{plainnat}
\bibliography{bibliography}
\end{document}

And this is the entry from my bibliography.bib file:

@Book{williamson,
author={David P Williamson, David B Shmoys},
year = {2010},
title = {The Design of Approximation Algorithms},
publisher = {Cambridge University Press},
}

Best Answer

The way described in Ingmar's answer is the preferred one, but you don't get a separating comma between authors when you have only two of them.

I would follow that way, but if you really want a comma to separate them, you have to enclose the comma in braces, so that BibTeX considers it as normal text, i.e.

@Book{williamson,
author={David P Williamson{,} David B Shmoys},
year = {2010},
title = {The Design of Approximation Algorithms},
publisher = {Cambridge University Press},
}

Output

enter image description here

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