It appears when I use add_subplot method to add a plot
> to a Figure object that it is NOT semi-logarithmic if I
> use semilogy method later.
Works for me...
import matplotlib.numerix as nx
from pylab import figure, show
fig = figure()
ax = fig.add_subplot(111)
x = nx.arange(0.01, 5.0, 0.01)
y = nx.exp(-x)
ax.semilogy(x,y)
show()