What could cause a plot fail in my code?

[Robert]

Hi,

I find a useful code snippet on link:

http://stackoverflow.com/questions/25126444/logistic-regression-in-pymc/34400966#34400966

but it has error on plot function. The error message is as following:
---------
%run "C:\Users\rj\pyprj\logic_regression0.py"
[-----------------100%-----------------] 10000 of 10000 complete in 12.6       secPlotting beta0
Plotting tau
Plotting betaSalad
Plotting sigma
---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
C:\Users\pyprj\logic_regression0.py in <module>()
     34 #m.sample(100000, 50000, 50)
     35 m.sample(10000, 5000, 50)
---> 36 pm.Matplot.plot(m)
     37 import matplotlib.pyplot as plt
     38 #plt.plot(m)

C:\Users\AppData\Local\Enthought\Canopy\User\lib\site- packages\pymc\Matplot.pyc in wrapper(pymc_obj, *args, **kwargs)
    339                     if args:
    340                         name = '%s_%s' % (args[0], variable.__name__)
--> 341                     f(data, name, *args, **kwargs)
    342             return
    343         except AttributeError:

C:\Users\AppData\Local\Enthought\Canopy\User\lib\site-packages\pymc\Matplot.pyc in plot(data, name, format, suffix, path,  common_scale, datarange, new, last, rows, num, fontmap, verbose)
    453             num=num * 2,
    454             last=last,
--> 455             fontmap=fontmap)
    456 
    457         if last:

C:\Users\AppData\Local\Enthought\Canopy\User\lib\site-packages\pymc\Matplot.pyc in wrapper(pymc_obj, *args, **kwargs)
    375 
    376         # If others fail, assume that raw data is passed
--> 377         f(pymc_obj, *args, **kwargs)
    378 
    379     wrapper.__doc__ = f.__doc__

C:\Users\AppData\Local\Enthought\Canopy\User\lib\site-packages\pymc\Matplot.pyc in histogram(data, name, bins, datarange, format, suffix, path, rows, columns, num, last, fontmap, verbose)
    576 
    577         # Generate histogram
--> 578         hist(data.tolist(), bins, histtype='stepfilled')
    579 
    580         xlim(datarange)

C:\Users\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\pyplot.py in hist(x, bins, range, normed, weights, cumulative, bottom, histtype, align, orientation, rwidth, log, color, label, stacked, hold, data, **kwargs)
   2956                       histtype=histtype, align=align, orientation=orientation,
   2957                       rwidth=rwidth, log=log, color=color, label=label,
-> 2958                       stacked=stacked, data=data, **kwargs)
   2959     finally:
   2960         ax.hold(washold)

C:\Users\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\__init__.py in inner(ax, *args, **kwargs)
   1809                     warnings.warn(msg % (label_namer, func.__name__),
   1810                                   RuntimeWarning, stacklevel=2)
-> 1811             return func(ax, *args, **kwargs)
   1812         pre_doc = inner.__doc__
   1813         if pre_doc is None:

C:\Users\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\axes\_axes.py in hist(self, x, bins, range, normed, weights, cumulative, bottom, histtype, align, orientation, rwidth, log, color, label, stacked, **kwargs)
   6192                         ymin = np.amin(m[m != 0])
   6193                         # filter out the 0 height bins
-> 6194                 ymin = max(ymin*0.9, minimum) if not input_empty else minimum
   6195                 ymin = min(ymin0, ymin)
   6196                 self.dataLim.intervaly = (ymin, ymax)

UnboundLocalError: local variable 'ymin' referenced before assignment 
/////////////

I have no clue at all on debug it. Could you help me?
Thanks,