No diagrams appear with feynmp-auto

Question

I get blank space and no diagrams with the following code working in Texmaker on Windows. The mp file has been created. I have run pdflatex command. The log file gives the version as pdfTeX, Version 3.14159265-2.6-1.40.18 (MiKTeX 2.9.6500 64-bit) (preloaded format=pdflatex 2017.11.7) Any help would be much appreciated:)

     \documentclass{article}
     \usepackage{feynmp-auto}
     \begin{document}
     \begin{fmffile}{simple_labels}
     \begin{fmfgraph*}(40,25)
     \fmfleft{i1,i2}
     \fmfright{o1,o2}
     \fmflabel{$e^-$}{i1}
     \fmflabel{$e^+$}{i2}
     \fmflabel{$e^+,\mu^+$}{o1}
     \fmflabel{$e^-,\mu^-$}{o2}
     \fmflabel{$i\sqrt{\alpha}$}{v1}
     \fmflabel{$i\sqrt{\alpha}$}{v2}
     \fmf{fermion}{i1,v1,i2}
     \fmf{fermion}{o1,v2,o2}
     \fmf{photon,label=$\gamma,,Z^0$}{v1,v2}
     \end{fmfgraph*}
     \end{fmffile}
     \end{document}

Answer 1

I could make it work by adding the force option and after compiling twice with pdflatex -shell-escape.

 \documentclass{article}
 \usepackage[force]{feynmp-auto} %<-added force
 \begin{document}
 \begin{fmffile}{simple_labels}
 \begin{fmfgraph*}(40,25)
 \fmfleft{i1,i2}
 \fmfright{o1,o2}
 \fmflabel{$e^-$}{i1}
 \fmflabel{$e^+$}{i2}
 \fmflabel{$e^+,\mu^+$}{o1}
 \fmflabel{$e^-,\mu^-$}{o2}
 \fmflabel{$i\sqrt{\alpha}$}{v1}
 \fmflabel{$i\sqrt{\alpha}$}{v2}
 \fmf{fermion}{i1,v1,i2}
 \fmf{fermion}{o1,v2,o2}
 \fmf{photon,label=$\gamma,,Z^0$}{v1,v2}
 \end{fmfgraph*}
 \end{fmffile}
 \end{document}