"""
Demo of the streamplot function with starting points.

This example shows how to fix the streamlines that are plotted, by passing
an array of seed points to the `start_points` keyword argument.
"""
import numpy as np
import matplotlib.pyplot as plt

Y, X = np.mgrid[-3:3:100j, -3:3:100j]
U = -1 - X**2 + Y
V = 1 + X - Y**2

# 5 points along the first diagonal and a point in the left upper quadrant
seed_points = np.array([[-2, -1, 0, 1, 2, -1], [-2, -1,  0, 1, 2, 2]])

fig, ax = plt.subplots()
strm = ax.streamplot(X, Y, U, V, color=U, linewidth=2,
                     cmap=plt.cm.autumn, start_points=seed_points.T)
fig.colorbar(strm.lines)

ax.plot(seed_points[0], seed_points[1], 'bo')

ax.axis((-3, 3, -3, 3))

plt.show()