Invert colors in qutip plot_wigner function

Question

In QuTiP, it is possible to plot Wigner functions with positive (shown in blue) and negative (shown in red) values.

For example, the following code displays the Wigner function of a Schrodinger cat state :

import matplotlib.pyplot as plt
from qutip import plot_wigner, coherent
N, alpha = 20, 2
fig, ax = plot_wigner(coherent(N, alpha)+coherent(N, -alpha))
plt.show()

Output:

Would it be possible to invert the color bar to get positive values in red and negative ones in blue ?

Answer 1

Adapted from this answer :

import numpy as np
import matplotlib.pyplot as plt
from matplotlib import cm
from matplotlib.colors import ListedColormap
from qutip import plot_wigner, coherent
# Red, Green, Blue
N = 256
vals = np.ones((N, 4))
# Blue stays constant until middle of colormap all other channels increase
# to result in white
# from middle of colormap we decrease to 255, 0, 0 which is red
inc = np.linspace(0, 1, N//2)
dec = np.linspace(1, 0, N//2)
cst = np.linspace(1, 1, N//2)
vals[:, 0] = np.concatenate((inc, cst), axis=None)
vals[:, 1] = np.concatenate((inc, dec), axis=None)
vals[:, 2] = np.concatenate((cst, dec), axis=None)
newcmp = ListedColormap(vals)
N, alpha = 20, 2
fig, ax = plot_wigner(coherent(N, alpha)+coherent(N, -alpha), cmap=newcmp)
plt.show()

Output