缺少 feynmf/feynmp 标签？

Question

我在用费因普使用 pdflatex 生成费曼图。一切似乎都正常，但我的标签没有显示出来。

怎么了？

\documentclass{minimal}
\usepackage{feynmp}

% Needed to interpret generated *.1, *.2 etc. as ps files.
\DeclareGraphicsRule{*}{mps}{*}{} 

\begin{document}
Here is a vertex for a local potential in momentum space:
\begin{fmffile}{fgraphs}
  \begin{fmfgraph}(40,30) 
    % Note that the size is given in normal parentheses instead of curly
    % brackets in units of \unitlength (default 1pt). 
    \fmfleft{i1,i2} % Define external vertices from bottom to top 
    \fmfright{o1,o2} 
    \fmf{fermion}{i1,v1,o1} 
    \fmf{fermion}{i2,v2,o2} 
    \fmf{photon,tension=0.3}{v1,v2}

    % These labels are missing! 
    \fmflabel{$\vec{p}$}{i1}
    \fmflabel{$\vec{q}$}{i2}
    \fmflabel{$\vec{p}+\vec{k}$}{o1}
    \fmflabel{$\vec{p}-\vec{k}$}{o2}
  \end{fmfgraph}
\end{fmffile}
\end{document}

保存tst.tex并编译：

pdflatex tst
mpost fgraphs
pdflatex tst
pdflatex tst

Answer 1

使用带星号的表格\begin{fmfgraph*}。