"""

=======

Buttons

=======

Constructing a simple button GUI to modify a sine wave.

The ``next`` and ``previous`` button widget helps visualize the wave with

new frequencies.

"""

import numpy as np

import matplotlib.pyplot as plt

from matplotlib.widgets import Button

freqs = np.arange(2, 20, 3)

fig, ax = plt.subplots()

fig.subplots_adjust(bottom=0.2)

t = np.arange(0.0, 1.0, 0.001)

s = np.sin(2*np.pi*freqs[0]*t)

l, = ax.plot(t, s, lw=2)

class Index:

ind = 0

def next(self, event):

self.ind += 1

i = self.ind % len(freqs)

ydata = np.sin(2*np.pi*freqs[i]*t)

l.set_ydata(ydata)

plt.draw()

def prev(self, event):

self.ind -= 1

i = self.ind % len(freqs)

ydata = np.sin(2*np.pi*freqs[i]*t)

l.set_ydata(ydata)

plt.draw()

callback = Index()

axprev = fig.add_axes([0.7, 0.05, 0.1, 0.075])

axnext = fig.add_axes([0.81, 0.05, 0.1, 0.075])

bnext = Button(axnext, 'Next')

bnext.on_clicked(callback.next)

bprev = Button(axprev, 'Previous')

bprev.on_clicked(callback.prev)

plt.show()

#############################################################################

#

# .. admonition:: References

#

# The use of the following functions, methods, classes and modules is shown

# in this example:

#

# - `matplotlib.widgets.Button`