Re: [Matplotlib-users] 'bug' in labelling axes for data with small variation?

[John H. <jdh...@ac...>]

>>>>> "Hans" == Hans Fangohr <H.F...@so...> writes:

  
    Hans> x=pylab.arange(0,1e-8,1e-9)+1.0 pylab.plot(x) pylab.show()

    Hans> All works fine when I subtract the mean of x but there seems
    Hans> to be a problem with labelling axes for plotted data which
    Hans> is not close to zero but shows only small variations.

I agree it's a bug.  It's not immediately clear to me what the labels
should be though

  1.0000000002
  1.0000000004
  1.0000000006

and so on?  That takes up a lot of room.  Granted, correct but ugly
is better than incorrect but pretty, but I'm curious if there is a
better way to format these cases.  Perhaps ideal would be an indicator
at the bottom or top of the y axis that read '1+' and then use 2e-9,
4e-9, etc as the actual tick labels.  Do you agree this is ideal?

To achieve this, as you may know, you can pass in a custom tick
formatter.  Eg

  import pylab

  def myformatter(x, pos):
      return '%1.0e'%(x-1)

  ax = pylab.subplot(111)
  x=pylab.arange(0,1e-8,1e-9)+1.0
  ax.plot(x)
  formatter = pylab.FuncFormatter(myformatter)
  ax.yaxis.set_major_formatter(formatter)
  ax.text(-.125, 1.025, '1+', transform=ax.transAxes)
  pylab.show()

See also examples/custom_ticker1.py.

This is not to say that I don't want to fix this bug; I just wanted to
make sure you are aware of this workaround.  

JDH