python - set_ydata for subplots OR why is figure containing two subplots significantly slower than figure without subpots -

i've extended following example use multiple subplots. here code:

#!/usr/bin/python import numpy np import matplotlib.pyplot  plt   matplotlib.widgets import slider ######################################## t = np.arange(0.0, 1.0, 0.001) a0 = 5 f0 = 3 s = a0*np.sin(2*np.pi*f0*t) ######################################## plt.close('all') fig, ax = plt.subplots(nrows=2, ncols=1) plt.subplots_adjust(bottom=0.30) ######################################## ax[0].plot(t,s, lw=2, color='red', label="red") ax[1].plot(t,s, lw=2, color='green', label="green") ######################################## # plt.axis([0, 1, -10, 10]) ax[0].set_xlim([0, 1]) ax[0].set_ylim([-10, 10])  ax[1].set_xlim([0, 1]) ax[1].set_ylim([-10, 10]) ######################################## axcolor = 'lightgoldenrodyellow' f1  = plt.axes([0.25, 0.20,  0.65, 0.03], axisbg=axcolor) a1  = plt.axes([0.25, 0.15, 0.65, 0.03], axisbg=axcolor)  f2  = plt.axes([0.25, 0.1,  0.65, 0.03], axisbg=axcolor) a2  = plt.axes([0.25, 0.05,  0.65, 0.03], axisbg=axcolor)  sf1 = slider(f1, 'freq1', 0.1, 30.0, valinit=f0) sa1 = slider(a1, 'amp1',  0.1, 10.0, valinit=a0)  sf2 = slider(f2, 'freq2', 0.1, 30.0, valinit=f0) sa2 = slider(a2, 'amp2',  0.1, 10.0, valinit=a0) ######################################## def update1(val):     amp  = sa1.val     freq = sf1.val      # not works - set_ydata not exists     # ax[1].set_ydata(amp*np.sin(2*np.pi*freq*t))     # ax[2].set_ydata(amp*np.sin(2*np.pi*freq*t))      # works seems slow     s = amp*np.sin(2*np.pi*freq*t)     ax[0].clear()     ax[0].plot(t,s, lw=2, color='red', label="red")     ax[0].set_xlim([0, 1])     ax[0].set_ylim([-10, 10])      # has no effect on speed     fig.canvas.draw_idle()  sf1.on_changed(update1) sa1.on_changed(update1)   def update2(val):     amp  = sa2.val     freq = sf2.val      # not works - set_ydata not exists     # ax[1].set_ydata(amp*np.sin(2*np.pi*freq*t))     # ax[2].set_ydata(amp*np.sin(2*np.pi*freq*t))      # works seems slow     s = amp*np.sin(2*np.pi*freq*t)     ax[1].clear()     ax[1].plot(t,s, lw=2, color='green', label="green")     ax[1].set_xlim([0, 1])     ax[1].set_ylim([-10, 10])      # has no effect on speed     fig.canvas.draw_idle()  sf2.on_changed(update2) sa2.on_changed(update2)  plt.show() 

the problem is slower (when slider clicked) original. suspect caused bunch of code used in update1 , update2 functions. not know how rewrite more effectively. original example using set_ydata function seems subplots not have function. i've been thinking 1 update function 4 sliders, not know if possible distinguish object on update triggered , handle inside function. thanks

you try call set_ydata on ax[0] (or ax[1], respectively). not work, these axes instances. set_ydata method of line2d artists. in example have linked line l created in beginning, receives new y data in update function. forgot in code.

so need create lines:

line0, = ax[0].plot(t,s, lw=2, color='red') line1, = ax[1].plot(t,s, lw=2, color='green') 

in beginning , in update functions can call:

line0.set_ydata(amp*np.sin(2*np.pi*freq*t)) 

or

line1.set_ydata(amp*np.sin(2*np.pi*freq*t)) 

note: idea here change y coordinates of lines. workaround, deleted entire graph , recreated it. more work , therefore makes things slower.