Bug in the rendering of the process matrix #2400
Description
Bug Description
The rendering of the process matrix looks weird in qutip-v5, The bottom of the bars behind is on top of the lower bars in front of it. (This is a CNOT gate with some errors)
Maybe the order of the bar rendering is reversed during the last refactoring of the plotting library?
Code to Reproduce the Bug
import numpy as np
import qutip
# Create a noisy CNOT gate
IZ = qutip.tensor([qutip.qeye(2), qutip.sigmaz()])
gate = qutip.gates.cnot()
noisy_gate = (-2.j * np.pi*(IZ/8/20)).expm() @ gate
fid = qutip.average_gate_fidelity(noisy_gate, qutip.gates.cnot())
print(f"noisy CNOT fidelity {fid}")
# Plot process matrix
op_basis = [[qutip.qeye(2), qutip.sigmax(), qutip.sigmay(), qutip.sigmaz()]] * 2
chi = qutip.qpt(qutip.to_super(noisy_gate), op_basis)
qutip.qpt_plot_combined(
chi, lbls_list=[["i", "x", "y", "z"]] * 2, title="Process Matrix"
)Code Output
noisy CNOT fidelity 0.9987669334932512
Expected Behaviour
The bars should be rendered correctly.
Your Environment
QuTiP Version: 5.0.1
Numpy Version: 1.26.4
Scipy Version: 1.12.0
Cython Version: None
Matplotlib Version: 3.8.3
Python Version: 3.11.8
Number of CPUs: 40
BLAS Info: Generic
INTEL MKL Ext: False
Platform Info: Linux (x86_64)Additional Context
No response