Python same colorbar for subplots of real / imaginary contour plots of function

Question

I am plotting a function z that is generated from a MWA like this:

import numpy as np
import matplotlib.pyplot as plt

ylist = np.linspace(0,10,20)
xlist = np.linspace(0,10,20)

zR = []                    # real part of z
zI = []                    # imaginary part of z

for y in ylist:
    for x in xlist:
        z = 0.2*x**2 + 1j*(x*y+0.7*np.sqrt(y))
        zR.append(z.real)
        zI.append(z.imag)

zR = np.array(zR)
z_matrixR = zR.reshape((ylist.size, xlist.size))

zI = np.array(zI)
z_matrixI = zI.reshape((ylist.size, xlist.size))

fig = plt.figure(figsize=(8.0,6.0))
ax1 = fig.add_subplot(221)    
z_contourR = ax1.contourf(xlist,ylist,z_matrixR,100)
plt.xlabel('x')
plt.ylabel('y')
plt.title('real')
#cbarR = plt.colorbar(z_contourR)

ax2 = fig.add_subplot(222)
z_contourI = ax2.contourf(xlist,ylist,z_matrixI,100)
plt.xlabel('x')
plt.ylabel('y')
plt.title('imaginary')
#cbarI = plt.colorbar(z_contourI)

plt.tight_layout()
plt.show()

I want both the real and imaginary parts of my z function to share the same colorbar, but I'm not sure how to do this. I have looked at this and this example, but am still unsure about how to apply it to my code.

score 3 · Accepted Answer · answered Dec 06 '15 at 21:50

vmin, vmax and levels are your friends. 3 options you may want:

use the same ones when plotting both real and imaginary parts

fig = plt.figure(figsize=(8.0,6.0))
ax1 = fig.add_subplot(221)    

vmax=30
vmin=0
levels = np.linspace(vmin,vmax,100)

z_contourR = ax1.contourf(xlist,ylist,z_matrixR,levels=levels,vmax=vmax,vmin=vmin)
plt.xlabel('x')
plt.ylabel('y')
plt.title('real')
cbarR = plt.colorbar(z_contourR)

ax2 = fig.add_subplot(222)
z_contourI = ax2.contourf(xlist,ylist,z_matrixI,levels=levels,vmax=vmax,vmin=vmin)
plt.xlabel('x')
plt.ylabel('y')
plt.title('imaginary')
cbarI = plt.colorbar(z_contourI)

plt.tight_layout()
plt.show()

the top right is white since it's out of the the levels I specified, you can get it back in by choosing a different maximum for levels and vmax this would create a funny looking colorbar but you might want it in some cases

fig = plt.figure(figsize=(8.0,6.0))
ax1 = fig.add_subplot(221)    

vmax=30
levels_max=100
vmin=0
levels = np.arange(vmin,levels_max,.1)

z_contourR = ax1.contourf(xlist,ylist,z_matrixR,levels=levels,vmax=vmax,vmin=vmin)
plt.xlabel('x')
plt.ylabel('y')
plt.title('real')
cbarR = plt.colorbar(z_contourR)

ax2 = fig.add_subplot(222)
z_contourI = ax2.contourf(xlist,ylist,z_matrixI,levels=levels,vmax=vmax,vmin=vmin)
plt.xlabel('x')
plt.ylabel('y')
plt.title('imaginary')
cbarI = plt.colorbar(z_contourI)

plt.tight_layout()
plt.show()

now, if you want both the top right filled and the color bar looking right you should redefine levels between drawings and plot both with the first color bar

fig = plt.figure(figsize=(8.0,6.0))
ax1 = fig.add_subplot(221)    

vmax=30
levels_max=30
vmin=0
levels = np.linspace(vmin,levels_max,100)

z_contourR = ax1.contourf(xlist,ylist,z_matrixR,levels=levels,vmax=vmax,vmin=vmin)
plt.xlabel('x')
plt.ylabel('y')
plt.title('real')
cbarR = plt.colorbar(z_contourR)

vmax=30
levels_max=100
vmin=0
levels = np.linspace(vmin,levels_max,100)


ax2 = fig.add_subplot(222)
z_contourI = ax2.contourf(xlist,ylist,z_matrixI,levels=levels,vmax=vmax,vmin=vmin)
plt.xlabel('x')
plt.ylabel('y')
plt.title('imaginary')
cbarI = plt.colorbar(z_contourR)

plt.tight_layout()
plt.show()

Python same colorbar for subplots of real / imaginary contour plots of function

1 Answers1