Define aspect ratio when using twinx

Have a look at the

adjustable

parameter of the axes. This controls whether
the data limits or the bounding rectangle’s shape are changed when the
aspect/limits are changed.

Normally, the options are

"box"

and

"datalim"

, but there’s a special case
for shared axes. In your case, you want

adjustable='box-forced'

.

As a quick example (I took the liberty of simplifying things slightly, feel
free to use the separate

set_foo

methods if they’re clearer to you. If you
take that route, the method is

ax.set_adjustable

.):

import numpy as npimport matplotlib.pyplot as pltx = np.linspace(0,1.6,50) + 50.0fig, ax = plt.subplots()ax2 = ax.twinx()XLIM = [50.0, 51.6]YLIM = [0.0, 1.1, 0.0, 11.0]ax.plot(x,np.sin(x-50.0),'b')ax2.plot(x,np.cos(x-50.0)*10.,'r')ax.set(adjustable='box-forced',       xlim=XLIM, ylim=YLIM[:2],       xticks=np.arange(XLIM[0], XLIM[1], 0.2),       yticks=np.arange(YLIM[0], YLIM[1]+0.1, 0.1)[:-1],       aspect=(XLIM[1]-XLIM[0])/(YLIM[1]-YLIM[0]))ax2.set(adjustable='box-forced',        ylim=YLIM[2:],        yticks=np.arange(YLIM[2], YLIM[3]+1.0, 1.0),        aspect=(XLIM[1]-XLIM[0])/(YLIM[3]-YLIM[2]))ax.grid(True, which='major',linestyle='solid')plt.show()