Using a logarithmic axis and defining the axis range and its label

Sometimes, you have to visualize rather pathological funtions containing
divergencies and/or varying over a large parameter range. This is best done
using an appropriate axis. Here, we show a simple example how to do
this with PyX. ...

In order to change the properties of the graph axes, we have to create
appropriate instances of an axis class and pass them as keyword arguments to
the `graph.graphxy` constructor. A number of predefined axes is contained in
the `graph.axis` module. Here, we use a linear (abbreviated as
`graph.axis.lin`) and a logarithmic (abbreviated as `graph.axis.log`) axis. In
both cases, we pass a minimal and maximal value for the axis range. Whereas for
the x-axis this is not strictly necessary (we could as well tell the
`graph.data.function` instance to emit data in a certain x-range), it is
important for the y-axis because the function diverges for certain x values. If
we do not set the y range manually, we would obtain a rather compressed display
of the function in the y-direction, which, moreover, would strongly depend on
the sampling points choosen by PyX along the x-direction. Since the function only
diverges towards positive y-values, we only need to set the maximal value of
the y-axis (using the `max`-argument). Of course, you can also fix the lower end
of the axis range by providing a `min`-argument. In order to introduce the
`title` keyword, we give names to the axes.

! Note how PyX changes the way the x-axis is drawn. Instead of simple decimal
numbers, an exponential notation is used. This happens automatically by
default, if at least one of the values to be shown becomes 10,000 or bigger
smaller than 0.001. This behaviour can be altered by using a different axis
texter.
