Hi,

I have problems with streamplot

I want to use a 3d vector field in coordinates (x,y,z) stored in a numpy array, and plot slices of it with streamplot.

To test it I wanted to use a vector field with arrows pointed up in the z>0 region and pointed down in the z<0 region.

```
import numpy as np
import matplotlib.pyplot as plt
from math import *
max = 100
min = -100
X = np.linspace(min, max, num=100)
Y = np.linspace(min, max, num=100)
Z = np.linspace(min, max, num=100)
N = X.size
#single components in the 3D matrix
Bxa = np.zeros((N, N, N))
Bya = np.zeros((N, N, N))
Bza = np.zeros((N, N, N))
for i, x in enumerate(X):
for j, y in enumerate(Y):
for k, z in enumerate(Z):
Bxa[ i, j, k] = 0.0 #x
Bya[ i, j, k] = 0.0 #y
Bza[ i, j, k] = z
#I take a slice close to Y=0
Bx_sec = Bxa[:,N/2,:]
By_sec = Bya[:,N/2,:]
Bz_sec = Bza[:,N/2,:]
fig = plt.figure()
ax = fig.add_subplot(111)
ax.streamplot(X, Z, Bx_sec, Bz_sec, color='b')
ax.set_xlim([X.min(), X.max()])
ax.set_ylim([Z.min(), Z.max()])
plt.show()
```

But I obtain something that looks like if I have put Bza = x! I tried to invert the order of vectors but it is unuseful!

I attach the picture. Do you understand why? (the code I posted should run)

Gabriele