Matplotlib Second x-axis with converted values

Question

I used a piece of code (based on a solution to another problem posed here ) to create spectral data plots with two x-axis. The first (lower) is in frequency units, the second (upper) is simply converted to units of wavelength (wavelength = 3E8 / frequency). This worked fine until I upgraded MPL to 1.4.2, after which the values ​​on the upper axis will be the same as on the lower axis (see Example).

MWE (exact copy of the MPL mailing list):

from matplotlib.transforms import Transform, BlendedGenericTransform, IdentityTransform import matplotlib.pyplot as plt from mpl_toolkits.axes_grid.parasite_axes import SubplotHost import numpy as np c = 3.e2 class Freq2WavelengthTransform(Transform): input_dims = 1 output_dims = 1 is_separable = False has_inverse = True def transform(self, tr): return c/tr def inverted(self): return Wavelength2FreqTransform() class Wavelength2FreqTransform(Freq2WavelengthTransform): def inverted(self): return Freq2WavelengthTransform() aux_trans = BlendedGenericTransform(Freq2WavelengthTransform(), IdentityTransform()) fig = plt.figure(2) ax_GHz = SubplotHost(fig, 1,1,1) fig.add_subplot(ax_GHz) ax_GHz.set_xlabel("Frequency (GHz)") xvals = np.arange(199.9, 999.9, 0.1) #make some test data data = np.sin(0.03*xvals) ax_mm = ax_GHz.twin(aux_trans) ax_mm.set_xlabel('Wavelength (mm)') ax_mm.set_viewlim_mode("transform") ax_mm.axis["right"].toggle(ticklabels=False) ax_GHz.plot(xvals, data) ax_GHz.set_xlim(200, 1000) plt.draw() plt.show() 

This gives

Can I advise how to handle this in MPL 1.4.2?

Answer 1

Using a combination of the Adobe response from the stream associated with the wwii comment and your own code.

 import numpy as np import matplotlib.pyplot as plt c=3.e2 fig = plt.figure() ax1 = fig.add_subplot(111) ax2 = ax1.twiny() xvals = np.arange(199.9, 999.9, 0.1) data = np.sin(0.03*xvals) ax1.plot(xvals, data) ax1Ticks = ax1.get_xticks() ax2Ticks = ax1Ticks def tick_function(X): V = c/X return ["%.3f" % z for z in V] ax2.set_xticks(ax2Ticks) ax2.set_xbound(ax1.get_xbound()) ax2.set_xticklabels(tick_function(ax2Ticks)) ax1.set_xlabel("Frequency (GHz)") ax2.set_xlabel('Wavelength (mm)') ax1.grid(True) plt.ylim(ymin=-1.1,ymax=1.1) plt.show() 

This gives;

Hope this helps!