Why natbib package can not find author?

Question

I have a .bib file as following:

%% This BibTeX bibliography file was created using BibDesk.
%% http://bibdesk.sourceforge.net/
%% Saved with string encoding Unicode (UTF-8) 

@book{marcu2000theory,
    Author = {Marcu, Daniel},
    Date-Added = {2013-02-12 04:56:47 +0000},
    Date-Modified = {2013-02-12 04:56:47 +0000},
    Publisher = {MIT Press},
    Title = {The theory and practice of discourse parsing and summarization},
    Year = {2000}}

My Latex file:

\documentclass{article} % For LaTeX2e
\usepackage{graphicx}
\usepackage{url}
\usepackage{natbib}

\title{T}

\begin{document}
\maketitle
\cite{marcu2000theory}
\citeauthor{marcu2000theory}

\bibliography{DPSurvey}
\bibliographystyle{plain}

\end{document}

However, I always got the warning:

Author undefined for citation`marcu2000theory' (natbib) on page 1

Could someone point out the mistake?

Answer 1

Use natbib's replacement of plain style, plainnat.bst. And to have numerical citations, use the numbers options.

\usepackage[numbers]{natbib}
\bibliographystyle{plainnat}