same scale of Y axis on differents figures

Question

I try to plot different data with similar representations but slight different behaviours and different origins on several figures. So the min & max of the Y axis is different between each figure, but the scale too.

e.g. here are some extracts of my batch plotting :

Does it exists a simple way with matplotlib to constraint the same Y step on those different figures, in order to have an easy visual interpretation, while keeping an automatically determined Y min and Y max ?

In others words, I'd like to have the same metric spacing between each Y-tick

Answer 1

you could use a MultipleLocator from the ticker module on both axes to define the tick spacings:

import matplotlib.pyplot as plt
import matplotlib.ticker as ticker

fig=plt.figure()
ax1=fig.add_subplot(211)
ax2=fig.add_subplot(212)
ax1.set_ylim(0,100)
ax2.set_ylim(40,70)

# set ticks every 10
tickspacing = 10
ax1.yaxis.set_major_locator(ticker.MultipleLocator(base=tickspacing)) 
ax2.yaxis.set_major_locator(ticker.MultipleLocator(base=tickspacing))

plt.show()

EDIT:

It seems like your desired behaviour was different to how I interpreted your question. Here is a function that will change the limits of the y axes to make sure ymax-ymin is the same for both subplots, using the larger of the two ylim ranges to change the smaller one.

import matplotlib.pyplot as plt
import numpy as np

fig=plt.figure()
ax1=fig.add_subplot(211)
ax2=fig.add_subplot(212)
ax1.set_ylim(40,50)
ax2.set_ylim(40,70)

def adjust_axes_limits(ax1,ax2):

    yrange1 = np.ptp(ax1.get_ylim())
    yrange2 = np.ptp(ax2.get_ylim())

    def change_limits(ax,yr):
        new_ymin = ax.get_ylim()[0] - yr/2.
        new_ymax = ax.get_ylim()[1] + yr/2.
        ax.set_ylim(new_ymin,new_ymax)

    if yrange1 > yrange2:
        change_limits(ax2,yrange1-yrange2)
    elif yrange2 > yrange1:
        change_limits(ax1,yrange2-yrange1)
    else:
        pass

adjust_axes_limits(ax1,ax2)
plt.show()

Note that the first subplot here has expanded from (40, 50) to (30, 60), to match the y range of the second subplot