two scale plots

how do I force the second plot to have the same limits on

    > the x axis as the first?

The short answer is you can't. You could write some helper functions
or classes to force axes to behave similarly. The example code below
will call any function on all the axes. Use with caution!

class CallAll:
    def __init__(self, seq, name):
        self.seq = seq = name

    def __call__(self, *args, **kwargs):
        for a in self.seq:
            func = getattr(a,
            func(*args, **kwargs)

class SharedAxes:

   def __init__(self, axlist):
       self.axlist = axlist

   def __getattr__(self, key):
       return CallAll(self.axlist, key)

ax1 = subplot(211)
plot(blah, blah)

ax2 = subplot(212)
plot(blah, blah)

shared = SharedAxes((ax1, ax2))