以对数比例绘图时，matplotlib辅助轴会反转。
在所附的例子中，我使用星等作为主（左）轴，亮度作为次（右）轴。较高的亮度应该对应较小的星等，就像在前两个图中一样。然而，在第三个图中，当我使用亮度的对数刻度时，亮度随着星等增加，这是不正确的。这是一个bug，还是我做错了什么？

# Test secondary axis
import numpy as np
import matplotlib
import matplotlib.pyplot as plt
print(matplotlib.__version__)

# Mag to luminosity (solar units) conversion
M_sun = 4.83

def mag2lum(mag):
    return 10**(0.4*(M_sun - mag))

def lum2mag(L):
    return M_sun - 2.5*np.log10(L)

def mag2lgl(mag):
    return 0.4*(M_sun - mag)

def lgl2mag(lgl):
    return M_sun - 2.5*lgl

# log luminosity as second axis - correct behaviour
fig, ax = plt.subplots(constrained_layout=True)
plt.ylabel(r'$M_G$ [mag]')
plt.xlim(-1, 5)
plt.ylim(10, 0)
secax = ax.secondary_yaxis('right', functions=(mag2lgl, lgl2mag))
secax.set_ylabel(r'$\log\ L_G\ [L_\odot]$')
plt.show()

# luminosity as second axis - correct behaviour, but labelling is horrible
fig, ax = plt.subplots(constrained_layout=True)
plt.ylabel(r'$M_G$ [mag]')
plt.xlim(-1, 5)
plt.ylim(10, 0)
secax = ax.secondary_yaxis('right', functions=(mag2lum, lum2mag))
secax.set_ylabel(r'$L_G\ [L_\odot]$')
plt.show()

# luminosity as second axis on log scale: axis is reversed
fig, ax = plt.subplots(constrained_layout=True)
plt.ylabel(r'$M_G$ [mag]')
plt.xlim(-1, 5)
plt.ylim(10, 0)
secax = ax.secondary_yaxis('right', functions=(mag2lum, lum2mag))
secax.set_ylabel(r'$L_G\ [L_\odot]$')
secax.set_yscale('log')
plt.show()

log luminosity as second axis - correct behaviourluminosity as second axis - correct behaviour, but labelling is horribleluminosity as second axis on log scale: axis is reversed
在第三个图中，光度应该向上增加。