# Quiver demo¶

Most examples work across multiple plotting backends, this example is also available for:

In [1]:
import numpy as np
import holoviews as hv
from holoviews import opts

hv.extension('matplotlib')


### Define data¶

In [2]:
xs, ys = np.arange(0, 2 * np.pi, .2), np.arange(0, 2 * np.pi, .2)
X, Y = np.meshgrid(xs, ys)
U = np.cos(X)
V = np.sin(Y)

# Convert to magnitude and angle
mag = np.sqrt(U**2 + V**2)
angle = (np.pi/2.) - np.arctan2(U/mag, V/mag)


## Matplotlib¶

In [3]:
label = 'Arrows scale with plot width, not view'

vectorfield = hv.VectorField((xs, ys, angle, mag))
vectorfield.relabel(label)

Out[3]:
In [4]:
label = "pivot='mid'; every third arrow"

vf_mid = hv.VectorField((xs[::3], ys[::3], angle[::3, ::3], mag[::3, ::3]))
points = hv.Points((X[::3, ::3].flat, Y[::3, ::3].flat))

opts.defaults(opts.Points(color='red'))

(vf_mid * points).relabel("pivot='mid'; every third arrow")

Out[4]:
In [5]:
label = "pivot='tip'; scales with x view"
vf_tip = hv.VectorField((xs, ys, angle, mag))
points = hv.Points((X.flat, Y.flat))

(vf_tip * points).opts(
opts.Points(s=5),
opts.VectorField(color='Magnitude', pivot='tip', magnitude='Magnitude', title=label))

Out[5]: