 # Trouble with contour plot

Hello,

I'm having a weird problem with a contour plot. Consider the following
plots:

import cPickle as pickle
import matplotlib.pyplot as plt
(Theta, Phi, Bnormal) = pickle.load(open('trouble.pickle', 'rb'))
plt.figure(0)
for i in [0, 300]:
plt.plot(Theta, Bnormal[:, i], label='Bnormal at Phi=%.3g' % Phi[i])

plt.ylabel('Theta')
plt.legend()
plt.savefig('figure0.png')
plt.figure(1)
plt.contourf(Phi, Theta, Bnormal)
plt.xlabel('Phi')
plt.ylabel('Theta')
plt.colorbar()
plt.savefig('figure1.png')

The 'trouble.pickle' file is available on
http://www.rath.org/trouble.pickle. At Phi=0 the contour plot agrees
with the crossection (both show an n=7 oscillation), but at Phi=1.68 the
contour plot shows a uniform value while the crossection shows a phase
shifted version of oscillation at Phi=0.

It seems to me that this is a blatant contradiction.

I have also uploaded the two figures at http://www.rath.org/figure1.png
and http://www.rath.org/figure0.png.

Am I missing something, or is this a bug?

\$ python --version
Python 2.6.5
\$ python -c 'import matplotlib; print matplotlib.__version__'
1.0.0

Thanks,

-Nikolaus

···

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Nikolaus,

What might be happening is that the Theta variable isn’t monotonic. It first goes from zero to pi, then from -pi to 0. This also explains the odd lines that appear in the line plots at the top and bottom. Try reforming your arrays so that the domain is monotonic (note that you will have to adjust the Phi and the Bnormal arrays as well because they were arranged assuming a certain domain from Theta.

Ben Root

···

On Thu, Oct 28, 2010 at 3:31 PM, Nikolaus Rath <Nikolaus@…3333…2…> wrote:

Hello,

I’m having a weird problem with a contour plot. Consider the following

plots:

import cPickle as pickle

import matplotlib.pyplot as plt

(Theta, Phi, Bnormal) = pickle.load(open(‘trouble.pickle’, ‘rb’))

plt.figure(0)

for i in [0, 300]:

``````plt.plot(Theta, Bnormal[:, i], label='Bnormal at Phi=%.3g' % Phi[i])
``````

plt.ylabel(‘Theta’)

plt.legend()

plt.savefig(‘figure0.png’)

plt.figure(1)

plt.contourf(Phi, Theta, Bnormal)

plt.xlabel(‘Phi’)

plt.ylabel(‘Theta’)

plt.colorbar()

plt.savefig(‘figure1.png’)

The ‘trouble.pickle’ file is available on

http://www.rath.org/trouble.pickle. At Phi=0 the contour plot agrees

with the crossection (both show an n=7 oscillation), but at Phi=1.68 the

contour plot shows a uniform value while the crossection shows a phase

shifted version of oscillation at Phi=0.

It seems to me that this is a blatant contradiction.

I have also uploaded the two figures at http://www.rath.org/figure1.png

Am I missing something, or is this a bug?

\$ python --version

Python 2.6.5

\$ python -c ‘import matplotlib; print matplotlib.version

1.0.0

Thanks,

-Nikolaus