\Header{axis}{Add an Axis to a Plot}
\keyword{aplot}{axis}
\begin{Usage}
\begin{verbatim}
axis(side, at, labels=TRUE, ...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\texttt{side}] an integer specifying which side of the plot
the axis is to be drawn on.
\item[\texttt{at}] the points at which tick-marks are to be drawn.
\item[\texttt{labels}] this can either be a logical value specifying
whether (numerical) annotations are to be made at
the tickmarks, or a vector of character strings to be placed
at the tickpoints.
\item[\texttt{...}] graphical parameters may also be passed as
arguments to this function.
\end{ldescription}
\end{Arguments}
\begin{Value}
This function is invoked for its side effect,
which is to add an axis to an already existing plot.
The axis is placed as follows:
1=below, 2=left, 3=above and 4=right.\end{Value}
\begin{Examples}
\begin{ExampleCode}
plot(1:4, rnorm(4), axes=FALSE)
axis(1, 1:4, LETTERS[1:4])
axis(2)
box() #- to make it look "as usual"

plot(1:7, rnorm(7), type = 's', xaxt='n', col = 'red')
axis(1, 1:7, LETTERS[1:7], col.axis = 'blue')
\end{ExampleCode}
\end{Examples}

