# matplotlib 3D图中的平面

I am trying to create a 3D plot with matplotlib, which represents the outer boundary of a specific domain. This boundary consists of an upper and lower surface, which is easy to visualize using the `plot_surface` method. My problem is to visualize the four flat surfaces which are parallel to the xz- and yz-planes (see attached image below). Since these surfaces also limit the domain I want them to be colored slightly transparent. My question is, how can I achieve this? A minimal working example for the upper and lower boundaries as well as an image which illustrates the desired outcome is attached below. Thank's for you kind help in advance!

``````import numpy as np
import matplotlib.pyplot as plt
from matplotlib import cm
from mpl_toolkits.mplot3d import Axes3D

# Values for g11up and g11dw
x = np.linspace(-1, 1, 50)

# Meshgrid
X, Y = np.meshgrid(x, x)
Z = 2 - (X**2 + Y**2)

# Create figure and axes
fig = plt.figure(figsize=(4, 4.5))
ax.set_xlabel(r'\$x\$')
ax.set_ylabel(r'\$y\$')
ax.set_zlabel(r'\$z\$')

# Plot the upper surface
ax.plot_surface(X, Y, -Z, cmap=cm.Blues, vmin=-2*Z.max(), vmax=Z.max(),
alpha=0.9, linewidth=0)

# Plot the lower surface
ax.plot_surface(X, Y, Z, cmap=cm.Blues, vmin=-2*Z.max(), vmax=Z.max(),
alpha=0.9, linewidth=0)

# Plot edges
z = 1-x**2