\subsection{Labels}

We have already seen several examples of how to draw labels.
One is to label the overall diagram, at the top or bottom.
The \bs centerline command (see the PHOTONBURST diagram in section 2.9.2)
is useful for this.

The way to include text within the picture is with the \verb@\put@ command.
This was done in the sample file in section 1.6.
The syntax is:
\begin{verbatim}

\put(<(x,y) co-ordinates of the lower left point of the text>){<text>}

\end{verbatim}

More complicated constructions are possible when used in conjunction
with the \LaTeX\ \bs framebox and \bs makebox commands (see the\LaTeX\ 
manual for details).  The ``text'' can be mathematical equations,
normal words or even other pictures.  As an example:

\begin{verbatim}

\begin{picture}(20000,8000)
\drawline\photon[\N\REG](3000,0)[5]
\put(4000,\pmidy){$\leftarrow \frac{ig_{\mu\nu}}{p^2-m^2+i\epsilon}$}
\put(2000,\pbacky){$\mu$}
\put(2000,\pfronty){$\nu$}
\end{picture}

\end{verbatim}
which results in

\begin{picture}(20000,8000)
\drawline\photon[\N\REG](3000,0)[5]
\put(4000,\pmidy){$\leftarrow \frac{ig_{\mu\nu}}{p^2-m^2+i\epsilon}$}
\put(2000,\pbacky){$\mu$}
\put(2000,\pfronty){$\nu$}
\end{picture}

\section{Review Exercise for Chapter Two}

Produce the following diagram, including labelling.  Note the styles
and boldness used.

%\begin{verbatim}

\begin{picture}(20000,20000)
\thicklines\drawline\photon[\SE\REG](18000,18000)[5]
\drawline\fermion[\S\REG](\photonfrontx,\photonfronty)[\boxlengthy]
\drawarrow[\N\ATBASE](\pmidx,\pmidy)
\drawline\fermion[\W\REG](\photonbackx,\photonbacky)[\photonlengthx]
\drawarrow[\W\ATTIP](\pmidx,\pmidy)
\thinlines\drawline\fermion[\S\REG](\fermionbackx,\fermionbacky)[150]
\drawline\fermion[\W\REG](\fermionfrontx,\fermionfronty)[150]
\drawline\fermion[\SW\REG](\fermionbackx,\fermionbacky)[7000]
\drawline\fermion[\S\REG](\fermionbackx,\fermionbacky)[75]
\drawline\fermion[\E\REG](\fermionbackx,\fermionbacky)[75]
\drawline\gluon[\SW\REG](\fermionbackx,\fermionbacky)[5]
\put(\gluonfrontx,\gluonfronty){\circle*{500}}
\drawline\fermion[\S\REG](\fermionbackx,\fermionbacky)[75]
\drawline\fermion[\E\REG](\fermionbackx,\fermionbacky)[75]
\drawline\fermion[\NE\REG](\fermionbackx,\fermionbacky)[7000]
\put(\gluonbackx,\gluonbacky){\circle*{500}}
\gaplength=300
\drawline\scalar[\NW\REG](\gluonbackx,\gluonbacky)[3]
\thicklines\drawarrow[\NW\ATBASE](\scalarbackx,\scalarbacky)
\gaplength=300   \thinlines
\drawline\scalar[\SE\REG](\gluonbackx,\gluonbacky)[3]
\put(\pfrontx,\scalarbacky){{\bf H}$^0$}
\put(\gluonfrontx,\gluonfronty)
{\ $\,{}_{\longleftarrow f_6(\omega,p_+\cdot q_-)}$}
\drawline\fermion[\NW\REG](\photonfrontx,\photonfronty)[2000]
\drawarrow[\NW\ATBASE](\pbackx,\pbacky)
\drawline\fermion[\SE\REG](\photonbackx,\photonbacky)[2000]
\drawarrow[\NW\ATTIP](\pmidx,\pmidy)
\put(\pbackx,\pbacky){$\,\,p+q$}
\end{picture}

%\end{verbatim}