loglog plot problem

Stephen_Walton · February 10, 2005, 7:15pm

I can't seem to get loglog plots to work. Attached is a dump of ipython showing what I tried and what happened. In case you don't want to wade through this, just try the following:

hold(False)
x=arange(25)+1
loglog(x,x**2) # throws error
close(1)
plot(log(x),log(x**2)) # works
close(1)
plot(x,x**2)
plot(log(x),log(x**2)) # throws error
loglog(x,x**2) # also throws error

Here's a result of doing something similar to the above manually, with traceback:

freyer:~> ipython -pylab
Python 2.3.4 (#1, Feb 2 2005, 12:11:53)
Type "copyright", "credits" or "license" for more information.

IPython 0.6.7 -- An enhanced Interactive Python.
? -> Introduction to IPython's features.
%magic -> Information about IPython's 'magic' % functions.
help -> Python's own help system.
object? -> Details about 'object'. ?object also works, ?? prints more.

  Welcome to pylab, a matplotlib-based Python environment
    help(matplotlib) -> generic matplotlib information
    help(pylab) -> matlab-compatible commands from matplotlib
    help(plotting) -> plotting commands

In [1]: x=arange(10)+1

In [2]: plot(x,x**2)
Out[2]: [<matplotlib.lines.Line2D instance at 0x410f132c>]

In [3]: loglog(x,x**2)

···

---------------------------------------------------------------------------
exceptions.ValueError Traceback (most recent call last)

/home/swalton/<console>

/usr/lib/python2.3/site-packages/matplotlib/pylab.py in loglog(*args, **kwargs)
   1869 hold(b)
   1870 else:
-> 1871 draw_if_interactive()
   1872
   1873 hold(b)

/usr/lib/python2.3/site-packages/IPython/genutils.py in wrapper(*args, **kw)
    686 def wrapper(*args,**kw):
    687 wrapper.called = False
--> 688 out = func(*args,**kw)
    689 wrapper.called = True
    690 return out

/usr/lib/python2.3/site-packages/matplotlib/backends/__init__.py in draw_if_interactive()
     39 def draw_if_interactive():
     40 draw_if_interactive._called = True
---> 41 __draw_int()
     42 # Flag to store state, so external callers (like ipython) can keep track
     43 # of draw calls.

/usr/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py in draw_if_interactive()
     56 figManager = Gcf.get_active()
     57 if figManager is not None:
---> 58 figManager.show()
     59
     60

/usr/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py in show(self)
    275 # anim.py requires this
    276 if sys.platform=='win32' : self.window.update()
--> 277 else: self.canvas.draw()
    278 self._shown = True
    279

/usr/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py in draw(self)
    140
    141 def draw(self):
--> 142 FigureCanvasAgg.draw(self)
    143 tkagg.blit(self._tkphoto, self.renderer._renderer, 2)
    144 self._master.update_idletasks()

/usr/lib/python2.3/site-packages/matplotlib/backends/backend_agg.py in draw(self)
    306 self.renderer = RendererAgg(w, h, self.figure.dpi)
    307 self._lastKey = key
--> 308 self.figure.draw(self.renderer)
    309
    310 def tostring_rgb(self):

/usr/lib/python2.3/site-packages/matplotlib/figure.py in draw(self, renderer)
    332
    333 # render the axes
--> 334 for a in self.axes: a.draw(renderer)
    335
    336 # render the figure text

/usr/lib/python2.3/site-packages/matplotlib/axes.py in draw(self, renderer)
   1167 if not self.get_visible(): return
   1168 renderer.open_group('axes')
-> 1169 self.transData.freeze() # eval the lazy objects
   1170 self.transAxes.freeze() # eval the lazy objects
   1171 if self.axison:

ValueError: Cannot take log of nonpositive value

In [4]: plot(log(x),log(x**2))
---------------------------------------------------------------------------
exceptions.ValueError Traceback (most recent call last)

/home/swalton/<console>

/usr/lib/python2.3/site-packages/matplotlib/pylab.py in plot(*args, **kwargs)
   1957 hold(b)
   1958 else:
-> 1959 draw_if_interactive()
   1960
   1961 hold(b)