Problem with semilog and low number

Jean-Baptiste> S?ll ! I am trying to plot very small number for
    Jean-Baptiste> the Y-axis on semilogy but they do not appear at
    Jean-Baptiste> all unless one of the value is higher Moreover the
    Jean-Baptiste> labels on the Y axis become 0 below 0.001

    >>> semilogy([1.0, 2.3, 3.3],[9.4e-05, 9.4e-05, 9.4e-05]) <-- does
    >>> not work
    Jean-Baptiste> [<matplotlib.lines.Line2D instance at 0x935255c>]
    >>> semilogy([1.0, 2.3, 3.3],[9.4e-04, 9.4e-05, 9.4e-05]) <---
    >>> work
    Jean-Baptiste> [<matplotlib.lines.Line2D instance at 0x940e964>]

S?ll Jean!

Thanks for this example. The relevant code which handles autoscaling
is in matplotlib.axis.autoscale_view. I wasn't handling the special
case where min=max for log scaling (though I do handle it for linear

Try this replacement code for and the functions decade_down
and decade_up and replace the autoscale_view function.

def decade_down(x):
    'floor x to the nearest lower decade'
    lx = math.floor(math.log10(x))
    return 10**lx

def decade_up(x):
    'ceil x to the nearest higher decade'
    lx = math.ceil(math.log10(x))
    return 10**lx

class Axis(Artist):

    def autoscale_view(self):
        'Try to choose the view limits intelligently'

        vmin, vmax = self.datalim.bounds()
        if self._scale=='linear':

            if vmin==vmax:
                (exponent, remainder) = divmod(math.log10(vmax - vmin), 1)
            except OverflowError:
                print >>sys.stderr, 'Overflow error in autoscale', vmin, vmax
            if remainder < 0.5:
                exponent -= 1
            scale = 10**(-exponent)
            vmin = math.floor(scale*vmin)/scale
            vmax = math.ceil(scale*vmax)/scale

            self.viewlim.set_bounds(vmin, vmax)
        elif self._scale=='log':
            if vmin==vmax:
                vmin = decade_down(vmin)
                vmax = decade_up(vmax)
                self.viewlim.set_bounds(vmin, vmax)

Let me know how this works for you,