# URL isn't displayed when using natbib and gerplain bibliographystyle

I would like to use following reference in my bibtex-file:

@online{Iyer,
author = {Iyer, Ratliff, Vijayan},
title = {Algorithms for Vertex Ranking of Weighted Graphs},
subtitle = {Research Experiences for Graduate Students in Combinatorics 2013},
url = {http://www.math.illinois.edu/~dwest/regs/rankwt.html},
organization = {University of Illinois},
year = {2013},
urldate = {02.05.2017},
}


Unfortunately the URL doesn't get displayed, only the title and the authors. I'm using the following

\usepackage[square]{natbib}
\bibliographystyle{gerplain}


If I change the bibliographystyle to plainnat, the URL appears, but I have to use the gerplain. Do you have any ideas, what could be a problem?

• (1) welcome, (2) looking in the code, the URL field is not supported at all by that bibtex style. I would be surprised if it was even compatible with natbib. If you have to use this style, your best bet is probably to include the URL in the note field manually, including the formated URLDATE. The style originates from 1985(!) and does not seem to have been updated since 2003. – daleif Aug 17 '17 at 6:03
• That entry is for the modern biblatex system, it cannot be used with the older bibtex system by default. The urldate field has the wrong format. – Johannes_B Aug 17 '17 at 6:57

If, for some reason, you can't switch to using biblatex, you may want to look into using the natdin bibliography style instead of the ancient gerplain style. (URLs were not widely used at all in the late 1980s...) Oh, and do please correct the author field: use the keyword and (not commas) to separate authors, and do provide the authors' given names.

Several additional issues: since the natdin bibliography style doesn't recognize the entry type @online, the default or catch-all entry type @misc will be used for the entry at hand. Because the @misc entry type isn't programmed to recognize fields named subtitle, organization, and urldate, you should (a) combine the contents of the title and subtitle fields and (b) use the field names howpublished and note instead of organization and urldate, resp.

\RequirePackage{filecontents}
\begin{filecontents}{mybib.bib}
@online{Iyer,
author       = {Iyer, Ananth V. and Donald H. Ratliff and Gopalakrishanan Vijayan},
title        = {Algorithms for Vertex Ranking of Weighted Graphs. Research
Experiences for Graduate Students in Combinatorics 2013},
url          = {http://www.math.illinois.edu/~dwest/regs/rankwt.html},
howpublished = {University of Illinois},
year         = {2013},
note         = {Last checked: 2.5.2017},
}
\end{filecontents}

\documentclass{article}
\usepackage[ngerman]{babel}
\usepackage[square,numbers]{natbib}
\bibliographystyle{natdin}
\usepackage[spaces,obeyspaces,hyphens]{url}

\begin{document}
\cite{Iyer}
\bibliography{mybib}
\end{document}