Closed
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8000
!--/$-->Description
Bug summary
I get a broken colorbar (see Outcome below) when using contourf and specifiying colors with cmap and norm instead of colors, and requesting a proportional colorbar, and using extend
Code for reproduction
import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl
# Data definition and plot based on the Official contourf demo
# https://matplotlib.org/stable/gallery/images_contours_and_fields/contourf_demo.html
origin = 'lower'
delta = 0.025
x = y = np.arange(-3.0, 3.01, delta)
X, Y = np.meshgrid(x, y)
Z1 = np.exp(-X**2 - Y**2)
Z2 = np.exp(-(X - 1)**2 - (Y - 1)**2)
Z = (Z1 - Z2) * 2
nr, nc = Z.shape
fig2, ax2 = plt.subplots()
# Original demo levels
# levels = [-1.5, -1, -0.5, 0, 0.5, 1]
# Irregular levels because we want to use a colorbar with
# spacing='proportional'
levels = [-1.25, -0.5, -0.125, 0.125, 0.5, 1.25]
# Define a colormap and norm instead of using 'colors=' in the
# contourf call, BECAUSE we want to use the same cmap and norm for
# scatter and pcolormesh plots
cmap = mpl.colors.ListedColormap(['r', 'g', 'white', 'g', 'r'])
cmap.set_under('yellow')
cmap.set_over('cyan')
norm = mpl.colors.BoundaryNorm(levels, cmap.N)
CS3 = ax2.contourf(X, Y, Z, levels,
# NO PROBLEM with spacing='proportional' if we
# define the colors with 'colors='
#
# colors=('r', 'g', 'b'),
# The problem appears when we use cmap and norm
cmap=cmap,
norm=norm,
origin=origin,
# NO PROBLEM with spacing='proportional' if we dont
# use extend
# extend='min'
extend='both'
)
# Our data range extends outside the range of levels; make
# data below the lowest contour level yellow, and above the
# highest level cyan:
# CS3.cmap.set_under('yellow')
# CS3.cmap.set_over('cyan')
ax2.set_title('Listed colors')
# Notice that the colorbar gets all the information it
# needs from the ContourSet object, CS3.
fig2.colorbar(CS3,
# BROKEN colorbar if we use proportional spacing
spacing='proportional',
# spacing='uniform',
)
fig2.savefig('test_cb.png')
plt.show()Actual outcome
I get the following warning
/home/share/unix_files/cdat/miniconda3_21-02/envs/cdatm_py3/lib/python3.8/site-packages/matplotlib/colorbar.py:1083: RuntimeWarning: invalid value encountered in double_scalars
automin = (y[2] - y[1]) / clen
/home/share/unix_files/cdat/miniconda3_21-02/envs/cdatm_py3/lib/python3.8/site-packages/matplotlib/colorbar.py:1084: RuntimeWarning: invalid value encountered in double_scalars
automax = (y[-2] - y[-3]) / clen
and a broken colorbar looking like
Expected outcome
The colorbar is OK if I do use not all the ands specified above. Example below with spacing='uniform' instead of proportional
Operating system
CentOS Linux release 7.9.2009 (Core)
Matplotlib Version
3.3.4
Matplotlib Backend
'Qt5Agg' and 'Agg'
Python version
3.8.8
Jupyter version
No response
Other libraries
No response
Installation
conda
Conda channel
conda-forge