CODEWITHSUNDEEP
pythonmatplotlibcontour
Leonardo Araujo
Leonardo Araujo

Reputation: 124

Contourplot in matplot showing incorrect linestyle

I'm plotting a 2D matrix, which has positive and negative values, in matplotlib using contourplot. It is supposed to show solid lines for positive values and dashed lines for negative values:

loc = matplotlib.ticker.MaxNLocator(20)
Z = psi
lvls = loc.tick_values(Z.min(), Z.max())
fig, ax = plt.subplots(figsize=(7,7))
cp = plt.contour(X, Y, Z, 20, colors='k', linestyles=where(lvls >= 0, "-", "--"))
plt.xlabel('X')
plt.ylabel('Y')
plt.clabel(cp, inline=True, fontsize=10)
plt.gca().set_aspect('equal', adjustable='box')
plt.title('Stream function - Re = ' + str(Re) + ', t = {:.2f}'.format((t)*dt))
plt.savefig('SF' + '_Re' + str(Re) + '_N' + str(nx) + '_o' + str(order) + '_SF' + '.png')
plt.close()

However, this is what this code is plotting: Contour plot

As you can see, there are dashed lines where it is supposed to show solid lines and solid lines where it is supposed to show dashed lines. Any ideas?

Edit: the code below works just fine:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.ticker

nx = 100
ny = 100

# Generate 2D mesh
x = 2*np.pi*np.arange(0,nx,1)/(nx)
#x = linspace(0,Lx,nx,endpoint=True)
y = 2*np.pi*np.arange(0,ny,1)/(ny)
#y = linspace(0,Ly,ny,endpoint=True)
X, Y = np.meshgrid(x, y,indexing='ij')

Z = -np.sin(X/2)*np.cos(Y**1.5)

loc = matplotlib.ticker.MaxNLocator(20)
lvls = loc.tick_values(Z.min(), Z.max())
fig, ax = plt.subplots(figsize=(7,7))
cp = plt.contour(X,Y,Z,20, colors='k', linestyles=np.where(lvls >= 0, "-", "--"))
plt.clabel(cp, inline=True, fontsize=10)
plt.gca().set_aspect('equal', adjustable='box')
plt.show()

The output:

Example

Upvotes: 2

Views: 1739

Answers (1)

Sheldore
Sheldore

Reputation: 39042

You should switch the order of the line styles. Currently, your condition will assign - (solid line) to contours where lvls >= 0 otherwise it will assign -- (dashed line). That's how the where argument works.

In pseudo form, np.where(condition, A, B) means if condition is True assign A else assign B

Your present code (Not desired):

linestyles=np.where(lvls >= 0, "-", "--")

Right style (desired style):

linestyles=np.where(lvls >= 0, "--", "-")

Upvotes: 1

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