Streamplot ignores rightmost column and topmost row of velocity data #11452
Description
Bug report
Bug summary
streamplot ignores the rightmost column (and topmost row) in U and V and replaces them by a copy of the second to last column (row). This yields wrong stream lines in the rightmost column and topmost row of cells. The issue is most noticeable on coarse grids. (see example plots)
Code for reproduction
import numpy as np
import matplotlib.pyplot as plt
x = np.linspace(-1, 1, 3)
y = np.linspace(0, 1, 2)
U = np.array([[.2,.2,.2],[.2,1,.2]])
V = np.array([[-1,2,-1],[-1,0.,-1]])
plt.streamplot(x,y, U,V)
plt.quiver(x,y, U,V)
plt.xlim(-1.5,1.5)
plt.ylim(-0.5,1.5)
plt.savefig('StreamPlotIssue1.png')
plt.close()
x = np.linspace(-1, 1, 5)
y = np.linspace(0, 1, 4)
U = np.array([[.2,.2,.2,.2,.2],[.2,.2,.2,.2,.2],[.2,.2,.2,.2,.2],[.2,1.,1.,1,.2]])
V = np.array([[-1,.5,2,.5,-1],[-1,.5,2,.5,-1],[-1,.5,2,.5,-1],[-1,0.,0.,0.,-1]])
plt.streamplot(x,y, U,V)
plt.quiver(x,y, U,V)
plt.xlim(-1.5,1.5)
plt.ylim(-0.5,1.5)
plt.savefig('StreamPlotIssue2.png')
plt.close()Actual outcome
The first image uses just 2 cells (2 in x, 1 in y direction). The field should create an antisymmetric wave. The left cell is OK, the right one is garbage. (The example is chosen such that the top row issue doesn't show too badly). The overlaid quiver plot shows the correct velocity.
The second image uses 4 cells in x and 3 cells in y-direction for the same velocity field. Quiver shows the correct velocity as overlay. The rightmost column and top row of cells show the wrong streamlines.
For quick reference: the variables used
# image 1
#x:
[-1. 0. 1.]
# y:
[0. 1.]
# U:
[[0.2 0.2 0.2]
[0.2 1. 0.2]]
# V:
[[-1. 2. -1.]
[-1. 0. -1.]]
# image 2
#x:
[-1. -0.5 0. 0.5 1. ]
# y:
[0. 0.33333333 0.66666667 1. ]
# U:
[[0.2 0.2 0.2 0.2 0.2]
[0.2 0.2 0.2 0.2 0.2]
[0.2 0.2 0.2 0.2 0.2]
[0.2 1. 1. 1. 0.2]]
# V:
[[-1. 0.5 2. 0.5 -1. ]
[-1. 0.5 2. 0.5 -1. ]
[-1. 0.5 2. 0.5 -1. ]
[-1. 0. 0. 0. -1. ]]
Expected outcome
A streamline plot consistent with velocity shown in quiver overlay.
Matplotlib version
- Operating system:
MacOS High Sierra (10.13.5) - Matplotlib version:
matplotlib-2.1.2-py36h6d6146d_0 - Matplotlib backend (
print(matplotlib.get_backend())):
MacOSX - Python version:
3.6 - Jupyter version (if applicable):
n/a - Other libraries:
numpy
Python and matplotlib installed using anaconda3 package