CODEWITHSUNDEEP
pythongraphmatplotlib
user3494103
user3494103

Reputation:

Creating Matplotlib Graph with common line across subplots in Python

For an upcoming assignment I am require to make a series of diagrams that have two graphs that have a line going across from one graph to the other, colouring an area below that line on the other graph.

As shown in this rough drawing:

enter image description here

This is what I currently have: enter image description here

From this code:

from matplotlib import pyplot as plt

fig = plt.figure()
ax1 = fig.add_subplot(121)
ax1.plot([0,1,2,3,4,5,6,7,8,9,10], [1,1,1,1,1,0,0,0,0,0,0], '-b')
ax1.plot([0,1,2,3,4,5,6,7,8,9,10], [0,0,0,0,0,1,1,1,1,1,1], '-r')
ax1.set_ylim([0, 1.2])

ax2 = fig.add_subplot(122)
ax2.plot([0,5,10,15,20,25,30,35,40], [1,1,1,1,0,0,0,0,0], '-b')
ax2.plot([0,5,10,15,20,25,30,35,40], [0,0,0,0,1,1,1,1,1], '-r')
ax2.set_ylim([0, 1.2])

plt.show()

Obviously this only generates the two graphs and I have yet been unable to add the line across the two graphs.

I really want to be able to do this with Matplotlib in python with the ability to change the value (45 in the example case) and the coloured area change automatically.

Thanks!

Upvotes: 2

Views: 770

Answers (1)

CT Zhu
CT Zhu

Reputation: 54340

There are three steps: 1st, find the intercept point between green and blue lines in the left panel. 2nd, find the intercept point between the red and lines in the right panel. 3rd, fill the area between. These steps involves np.interp scipy.interpolat scipy.optimize and plt.fill_between, which you should look up.

from matplotlib import pyplot as plt
import numpy as np
import scipy.interpolate as spinp
import scipy.optimize as spop

fig = plt.figure(figsize=(16,4))
ax1 = fig.add_subplot(121)
x  = [0,10,20,30,40,50,60,70,80,90,100]
yr = [1,1,1,1,1,0,0,0,0,0,0]
yg = [0,0,0,0,0,1,1,1,1,1,1]
turn_pt = np.interp(45, x, yr) #change 45 to whatever.
yb = [0.,turn_pt,turn_pt]
ax1.plot(x, yr, '-r')
ax1.plot(x, yg, '-g')
xb = [45, 45, 200]
ll = plt.plot(xb,yb, '-b')
ll[0].set_clip_on(False) 
plt.axis([0,100,0,1.2])
#the above three lines to draw the line out of the box.

ax2 = fig.add_subplot(122)
yr = [1,1,1,1,0,0,0,0,0]
yg = [0,0,0,0,1,1,1,1,1]
x  = [0,5,10,15,20,25,30,35,40]
brk_pt_f = lambda X, V: (spinp.interp1d(x, yr)(X)-V)**2
brk_pt = spop.fmin(brk_pt_f, 17., args=(turn_pt,), disp=0) #17. is you inital guess,
#the above two lines solve for the intersection between the blue line and the red line
zero_pt = 20.
start_pt= 0.
xb = np.hstack((start_pt, brk_pt, zero_pt))
yb = [turn_pt,turn_pt,0]
ax2.plot(x, yr, '-r')
ax2.plot(x, yg, '-g')
ax2.plot(xb, yb, '-b')
ax2.hlines(turn_pt,0, 40, 'b', alpha=0.)
ax2.fill_between(xb, yb, 0, alpha=0.4)
ax2.set_ylim([0, 1.2])
ax2.set_xlim([0, 40])

enter image description here

There are a few solutions to get rid of the top x-axis and the right y-axis, please search older SO posts.

And finally, welcome to SO.

Upvotes: 2

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