[Matplotlib-users] double x-axis with defined xtick and inverse order

[Diego Avesani]

Dear all,

I would like to plot a figure with double x-axes.
Unfortunately, it seems the ticks of the second x axis do not fit with what
I want.

Here the example:

import numpy as np
import matplotlib.pyplot as plt

MM = np.array([ 1.,  2.,  4.,  8., 16., 32.])
SS = np.array([64., 32., 16.,  8.,  4.,  2.])
RR = np.array([2813, 1544,  895,  562,  459,409])

ax = plt.subplot(111)
ax.grid(True,which="both",ls="-",color='0.6')
ax.plot(MM, RR  ,'-r')

ax2 = ax.twiny()
ax2.invert_xaxis()
ax2.plot(MM, RR, 'none')
ax2.set_xticks([64,32,16,8,4,2])
ax2.set_xticklabels(['64','32','16','8','4','2'])
plt.show()

As it can be noticed, the value 32 in the ax2 does not correspond to the
second value but is put in the middle point of ax2. I would like to have it
in the same vertical line of the second value of MM.  This of course not
only for 32 but for the value in SS. Basically I would like to have the
main axis according to MM and a second ax with SS value in the same line of
MM values.

I hope I made myself clear.

really really thanks and,
best regards

Diego
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