Missing sphere in Bloch sphere animation example using Matplotlib Axes3D #2156
Description
Bug Description
I attempted to recreate this animation of the Bloch sphere using the instructions in the Plotting on the Bloch Sphere/Directly Generating an Animation section of the user guide. Using Matplotlib 3.4.3 gives a warning,
MatplotlibDeprecationWarning: Axes3D(fig) adding itself to the figure is deprecated since 3.4. Pass the keyword argument auto_add_to_figure=False and use fig.add_axes(ax) to suppress this warning. The default value of auto_add_to_figure will change to False in mpl3.5 and True values will no longer work in 3.6. This is consistent with other Axes classes.
The movie is produced fine. If I use Matplotlib 3.7.1, the movie file contains a white background and no drawn Bloch sphere; see here.
This issue appears to be fixed by modifying the line ax = Axes3D(fig, azim=-40, elev=30) in the example to ax = fig.add_subplot(111, projection="3d", elev=30, azim=-40).
Code to Reproduce the Bug
import numpy as np
import qutip
from matplotlib import pyplot, animation
from mpl_toolkits.mplot3d import Axes3D
def qubit_integrate(w, theta, gamma1, gamma2, psi0, tlist):
# operators and the hamiltonian
sx = qutip.sigmax()
sy = qutip.sigmay()
sz = qutip.sigmaz()
sm = qutip.sigmam()
H = w * (np.cos(theta) * sz + np.sin(theta) * sx)
# collapse operators
c_op_list = []
n_th = 0.5 # temperature
rate = gamma1 * (n_th + 1)
if rate > 0.0: c_op_list.append(np.sqrt(rate) * sm)
rate = gamma1 * n_th
if rate > 0.0: c_op_list.append(np.sqrt(rate) * sm.dag())
rate = gamma2
if rate > 0.0: c_op_list.append(np.sqrt(rate) * sz)
# evolve and calculate expectation values
output = qutip.mesolve(H, psi0, tlist, c_op_list, [sx, sy, sz])
return output.expect[0], output.expect[1], output.expect[2]
## calculate the dynamics
w = 1.0 * 2 * np.pi # qubit angular frequency
theta = 0.2 * np.pi # qubit angle from sigma_z axis (toward sigma_x axis)
gamma1 = 0.5 # qubit relaxation rate
gamma2 = 0.2 # qubit dephasing rate
# initial state
a = 1.0
psi0 = (a*qutip.basis(2, 0) + (1-a)*qutip.basis(2, 1))/np.sqrt(a**2 + (1-a)**2)
tlist = np.linspace(0, 4, 250)
#expectation values for ploting
sx, sy, sz = qubit_integrate(w, theta, gamma1, gamma2, psi0, tlist)
fig = pyplot.figure()
ax = Axes3D(fig, azim=-40, elev=30)
sphere = qutip.Bloch(axes=ax)
def animate(i):
sphere.clear()
sphere.add_vectors([np.sin(theta), 0, np.cos(theta)])
sphere.add_points([sx[:i+1], sy[:i+1], sz[:i+1]])
sphere.make_sphere()
return ax
def init():
sphere.vector_color = ['r']
return ax
ani = animation.FuncAnimation(fig, animate, np.arange(len(sx)),
init_func=init, blit=False, repeat=False)
ani.save('bloch_sphere.mp4', fps=20)Code Output
No response
Expected Behaviour
An animated Bloch sphere similar to the animation on the user guide here.
Your Environment
QuTiP Version: 4.7.1
Numpy Version: 1.23.5
Scipy Version: 1.10.1
Cython Version: None
Matplotlib Version: 3.7.1
Python Version: 3.11.2
Number of CPUs: 12
BLAS Info: INTEL MKL
OPENMP Installed: False
INTEL MKL Ext: True
Platform Info: Linux (x86_64)Additional Context
No response