New submission from Jianke SHI <shi.jianke.xh...@showadenko.com>:
Data 0 cannot be plotted by matplotlib.pyplot(3.3.4) just because some data is
less than 0 (python 3.8.8).
The following is a sample program to confirm the problem.
the left-bottom area in the right figure is not colored and remains transparent
just because the data z[2,2] is changed from 0 to -1.7E-13.
(see attached png file.)
I tried to trace the problem and find that the reason seems to be a bug in
ContourSet._get_lowers_and_uppers.(Line 1065 in contour.py(3.3.4))
if self.zmin == lowers[0]:
# Include minimum values in lowest interval
lowers = lowers.copy() # so we don't change self._levels
if self.logscale:
lowers[0] = 0.99 * self.zmin
else:
lowers[0] -= 1
while lowers[0] is the same as self.zmin, it will be reduced a little before
using. However, while lowers[0] is greater than self.zmin ( = -1.7E-13 ), it
will not be reduced and remains as it is.
I think the condition should be revised to self.zmin <= lowers[0]
from self.zmin == lowers[0].
(sample program)
import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline
z0 = np.array([[0., 0., 2.], [0., 0., 1.], [2., 1., 0.]])
z1 = np.array([[0., 0., 2.], [0., 0., 1.], [2., 1., -1.7E-13]])
fig = plt.figure(figsize=(2, 4))
ax0 = fig.add_subplot(121)
ax0.contourf(z0, cmap='jet')
ax0.set_aspect('equal')
ax1 = fig.add_subplot(122)
ax1.contourf(z1, cmap='jet')
ax1.set_aspect('equal')
plt.show()
----------
components: Library (Lib)
files: test_contourf_jet4r.png
messages: 403579
nosy: Klam
priority: normal
severity: normal
status: open
title: Data 0 cannot be plotted by matplotlib.pyplot just because some data is
less than 0. (ContourSet._get_lowers_and_uppers)
type: behavior
versions: Python 3.7, Python 3.8
Added file: https://bugs.python.org/file50337/test_contourf_jet4r.png
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<https://bugs.python.org/issue45422>
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