[Tex/LaTex] Missing labels on Feynman Graph using feynmf

feynmfmetafont

I'm trying to create a Feynman graph using the feynmf package. My minimal example is 

\documentclass{article}

\usepackage{feynmf}

\begin{document}

\begin{fmffile}{diagram}

  \begin{fmfgraph*}(40,25)
    \fmfleft{i1,i2}
    \fmfright{o1,o2}
    \fmfbottom{b}
    \fmf{fermion}{i2,v1,o2}
    \fmf{photon}{v1,b}
    \fmflabel{i1}{i1}
    \fmflabel{i2}{i2}
    \fmflabel{o1}{o1}
    \fmflabel{o2}{o2}
    \fmflabel{b}{b}
  \end{fmfgraph*}

\end{fmffile}

\end{document}

After compiling once, I have the graph but not the labels (as expected, I guess…). I get the error

pdflatex> feynmf: Label file diagram.t1 not found:

pdflatex> feynmf: Process diagram.mf with METAFONT and then reprocess this file.

OK, so I do as told and try to process the .mf file with Metafont in my terminal (using Xubuntu) with

mpost diagram.mf

And then I get stuck. It starts then stops with a question mark, and I don't know how to proceed or what Metapost is trying to tell me:

This is MetaPost, version 1.803 (kpathsea version 6.1.1)
(mpost.mp (/usr/share/texlive/texmf-dist/metapost/base/plain.mp
Preloading the plain mem file, version 1.004) ) (./diagram.mf
(/usr/share/texmf/metafont/feynmf/feynmf.mf
>> mode_setup
! Isolated expression.
<to be read again> 
                   ;
l.117 mode_setup;

?

Can anyone help? How can I get my labels?
Thanks a lot!

Best Answer

The program to call is not Metapost, but Metafont:

mf diagram.mf

However, it's better to use feynmp that has the same syntax and produces Metapost files: you'll get diagram.mp and running mpost diagram.mp will do.

There's another possibility:

\documentclass{article}

\usepackage{feynmp-auto} % or \usepackage{feynmp}

\begin{document}

\begin{fmffile}{diagram}

  \begin{fmfgraph*}(40,25)
    \fmfleft{i1,i2}
    \fmfright{o1,o2}
    \fmfbottom{b}
    \fmf{fermion}{i2,v1,o2}
    \fmf{photon}{v1,b}
    \fmflabel{i1}{i1}
    \fmflabel{i2}{i2}
    \fmflabel{o1}{o1}
    \fmflabel{o2}{o2}
    \fmflabel{b}{b}
  \end{fmfgraph*}

\end{fmffile}

\end{document}

The package feynmp-auto (which I'm the author of) even avoids the need of running manually mpost: the diagram is compiled at the end of a run (with pdflatex only if the source has been modified in the current LaTeX run) and will correctly place it at the next LaTeX run.

enter image description here

Related Question