Verified Commit f2acc4c7 authored by Christian Rohlfing's avatar Christian Rohlfing
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GDET3 Convolution GUI: Swap s(t) and h(t)

parent 1ecb06ad
%% Cell type:code id: tags:
``` python
# Copyright 2020 Institut für Nachrichtentechnik, RWTH Aachen University
%matplotlib widget
import ipywidgets as widgets
from ipywidgets import interact, interactive, fixed, Layout
from IPython.display import clear_output, display, HTML
import matplotlib.pyplot as plt
import numpy as np
from scipy import signal # convolution
import rwth_nb.plots.mpl_decorations as rwth_plots
from rwth_nb.misc.signals import *
```
%% Cell type:markdown id: tags:
<div>
<img src="figures/rwth_ient_logo@2x.png" style="float: right;height: 5em;">
</div>
# Demonstrator Faltung
Zum Starten: Im Menü: Run <span class="fa-chevron-right fa"></span> Run All Cells auswählen.
## Einleitung
Im Folgenden wird das Faltungsintegral
$$g(t)
= s(t)\ast h(t)
= \int\limits_{-\infty}^{\infty} s(\tau) h(t-\tau) \,\mathrm{d}\tau
$$
betrachtet.
%% Cell type:markdown id: tags:
## Demo
Wähle $s(t)$ und $h(t)$ sowie jeweils Verschiebung $t_0$ und Dehnungsfaktor $T$ für beide Signale: $s\left(\frac{t-t_0}{T}\right)$ und $h\left(\frac{t-t_0}{T}\right)$.
Zusätzlich zu Elementarsignalen kann auch eine frei definierbare Funktion $s_0(t)$ zur Faltung verwendet werden.
%% Cell type:code id: tags:
``` python
s_0 = lambda t: rect(t/2-1/2)*(-t)
```
%% Cell type:code id: tags:
``` python
def convolution(s, h):
# Convolve s and h numerically
return signal.convolve(s(tau), h(tau), mode='same')*deltat
(tau,deltat) = np.linspace(-15, 15, 10001, retstep=True) # tau axis
interval_cnt = 0; # Interval counter for stepwise plot
# Signals
signal_types = {
'Rechteck' : lambda t: rect(t/1.01), # slightly wider rect than usual, hotfix for stepwise demo
'Dreieck' : tri,
'Sprungfunktion' : unitstep,
'si-Funktion' : lambda t: si(t*np.pi),
'Exponentialimpuls' : lambda t: unitstep(t)*np.exp(-t),
'Gauß-Signal' : gauss,
'Doppelrechteck' : lambda t: rect(t*2+0.5)-rect(t*2-0.5),
'Rampe' : lambda t: t*rect(t-0.5),
'Versch. Rechteck' : lambda t: -rect(t-0.5),
'Eigene Kreation s0(t)' : s_0,
}
# Plot
fig0, axs0 = plt.subplots(1, 2, figsize=(12,2))
def update_signals(s_type, s_T, s_t0, h_type, h_T, h_t0):
# Get s(t) and h(t)
global s, h, gt, intervals_g # reused in second interactive plot
s = lambda tau: signal_types[s_type]((tau-s_t0)/s_T); # signal on time axis (shifted by t0 and stretched by T)
h = lambda tau: signal_types[h_type]((tau-h_t0)/h_T);
#intervals_s = np.array(signal_intervals[w_s_type.value])*s_T + s_t0; # get signal intervals and map to time axis (shifted by t0 and stretched by T)
#intervals_h = np.array(signal_intervals[w_h_type.value])*h_T + h_t0;
intervals_s,_,_ = find_intervals(s(tau), tau, 0.49*np.max(np.abs(s(tau)))/deltat, deltat)
intervals_h,_,_ = find_intervals(h(tau), tau, 0.49*np.max(np.abs(h(tau)))/deltat, deltat)
# Get g(t) = s(t) \ast h(t)
gt = convolution(s, h) # numerical convolution
intervals_g = np.unique(np.tile(intervals_h, len(intervals_s)) + np.repeat(intervals_s, len(intervals_h))) # intervals of g(t)
if intervals_g.size == 0: #
intervals_g = np.concatenate([intervals_s, intervals_h])
# Plot
if not axs0[0].lines: # plot s(t) and g(t)
ax = axs0[0]; ax.plot(tau, s(tau), 'rwth:blue');
ax.set_xlabel(r'$\rightarrow t$'); ax.set_ylabel(r'$\uparrow s(t)$')
ax.set_xlim([-2.9, 2.9]); ax.set_ylim([-1.19, 1.19]); rwth_plots.axis(ax); rwth_plots.grid(ax);
ax = axs0[1]; ax.plot(tau, h(tau), 'rwth:blue');
ax.set_xlabel(r'$\rightarrow t$'); ax.set_ylabel(r'$\uparrow h(t)$')
ax.set_xlim(axs0[0].get_xlim()); ax.set_ylim(axs0[0].get_ylim()); rwth_plots.axis(ax); rwth_plots.grid(ax); fig0.tight_layout();
else: # update lines
axs0[0].lines[0].set_ydata(s(tau));
axs0[1].lines[0].set_ydata(h(tau));
try: # if convolution figure is already opened, update s(tau)
if axs[0].lines:
axs[0].lines[1].set_ydata(s(tau));
rwth_plots.update_ylim(axs[0], np.concatenate((h(tau), s(tau))), 0.19, 5); rwth_plots.update_ylim(axs[1], gt, 0.19, 5);
update_plot(-2) # update convolution plot
update_plot_intervals() # update interval lines
except: pass
rwth_plots.update_ylim(axs0[0], s(tau), 0.19, 5); rwth_plots.update_ylim(axs0[1], h(tau), 0.19, 5);
def swap_signals(b):
s_type = w_s_type.value; h_type = w_h_type.value; w_s_type.value = h_type; w_h_type.value = s_type;
s_T = w_s_T.value; h_T = w_h_T.value; w_s_T.value = h_T; w_h_T.value = s_T;
s_t0 = w_s_t0.value; h_t0 = w_h_t0.value; w_s_t0.value = h_t0; w_h_t0.value = s_t0;
# Widgets
w_s_type = widgets.Dropdown(options=list(signal_types.keys()), description=r'Wähle $s(t)$:')
w_s_T = widgets.FloatSlider(min=0.5, max=4, value=1, step=.1, description=r'Dehnung T', style=rwth_plots.wdgtl_style)
w_s_t0 = s_t0=widgets.FloatSlider(min=-2, max=2, value=0, step=.1, description=r'Verschiebung $t_0$', style=rwth_plots.wdgtl_style)
w_h_type = widgets.Dropdown(options=list(signal_types.keys()), description=r'Wähle $h(t)$:')
w_h_T = widgets.FloatSlider(min=0.5, max=4, value=1, step=.1, description=r'Dehnung T', style=rwth_plots.wdgtl_style)
w_h_t0 = s_t0=widgets.FloatSlider(min=-2, max=2, value=0, step=.1, description=r'Verschiebung $t_0$', style=rwth_plots.wdgtl_style)
w = widgets.interactive(update_signals, s_type=w_s_type, s_T=w_s_T, s_t0=w_s_t0, h_type=w_h_type, h_T=w_h_T, h_t0 = w_h_t0)
display(widgets.HBox((widgets.VBox((w_s_type, w_s_T, w_s_t0)), widgets.VBox((w_h_type, w_h_T, w_h_t0), layout=Layout(margin='0 0 0 100px'))))); w.update();
swap_s_h = widgets.Button(icon='arrows-h', description='Austauschen'); swap_s_h.on_click(swap_signals)
display(widgets.HBox((widgets.VBox((w_s_type, w_s_T, w_s_t0), layout=Layout(margin='0 50px 0 0')),
swap_s_h,
widgets.VBox((w_h_type, w_h_T, w_h_t0), layout=Layout(margin='0 0 0 50px'))))); w.update();
```
%% Cell type:markdown id: tags:
... und betrachte hier das Faltungsergebnis:
%% Cell type:code id: tags:
``` python
fig, axs = plt.subplots(2, 1, figsize=(12, 12/rwth_plots.fig_aspect)) # gridspec_kw = {'width_ratios':[3, 1]}
t_w = widgets.FloatSlider(min=-4, max=4, value=-2, step=.1, description='Verschiebung $t$', style=rwth_plots.wdgtl_style)
intervals_gt = np.array([t_w.min, t_w.max])
@widgets.interact(t=t_w,
show_integrand=widgets.Checkbox(value=True, description='Zeige Integrand', style=rwth_plots.wdgtl_style))
def update_plot(t, show_integrand=True):
global interval_cnt, intervals_gt
t_ind = np.where(tau>=t); t_ind = t_ind[0][0]; g_plot = gt.copy(); g_plot[t_ind:] = np.nan; # hide g(t') with t'>t
sh = s(tau)*h(t-tau) # integrand
interval_cnt = np.argwhere((intervals_gt[1:] > t) & (intervals_gt[:-1] <= t)); # interval
interval_cnt = 0 if interval_cnt.size == 0 else interval_cnt[0][0]; # check for end of interval
if not axs[0].lines: # Call plot() and decorate axes. Usually, these functions take some processing time
ax = axs[0]; ax.plot(tau, h(t-tau), 'rwth:blue', label=r'$h(t-\tau)$'); # plot h(t-tau)
ax.plot(tau, s(tau), 'rwth:green', label=r'$s(\tau)$'); # plot s(tau)
ax.plot(tau, sh, '--', color='rwth:orange', lw=1, label=r'$s(\tau)h(t-\tau)$'); # plot integrand
rwth_plots.annotate_xtick(ax, r'$t$', t, -0.1, 'rwth:blue', 15); # mark t on tau axis
ax.fill_between(tau, 0, sh, facecolor="none", hatch="//", edgecolor='rwth:black', linewidth=0.0); # hatch common area
ax.set_xlabel(r'$\rightarrow \tau$');
ax.set_xlim([-4.2,4.2]); rwth_plots.update_ylim(ax, np.concatenate((h(tau), s(tau))), 0.19, 5);
ax.legend(); rwth_plots.grid(ax); rwth_plots.axis(ax);
ax = axs[1]; ax.plot(tau, g_plot); # plot g(t)
ax.plot([t, t], [0, gt[t_ind]], 'ko--', lw=1);
ax.set_xlabel(r'$\rightarrow t$'); ax.set_ylabel(r'$\uparrow g(t)=s(t)\ast h(t)$');
ax.set_xlim(axs[0].get_xlim()); rwth_plots.update_ylim(ax, gt, 0.19, 5);
rwth_plots.grid(ax); rwth_plots.axis(ax); fig.tight_layout(); #plt.subplots_adjust(wspace=.1,hspace=.1)
else: # Replace only xdata and ydata since plt.plot() takes longer time
ax = axs[0]; ax.lines[0].set_ydata(h(t-tau)); ax.lines[2].set_ydata(sh); # update signals
ax.texts[0].set_x(t); ax.lines[3].set_xdata([t,t]) # update labels
if ax.collections: ax.collections[0].remove(); # update integrand
if show_integrand: ax.fill_between(tau,0,sh, facecolor="none", hatch="//", edgecolor='k', linewidth=0.0);
ax = axs[1]; ax.lines[0].set_ydata(g_plot); # update signals
ax.lines[1].set_xdata([t, t]); ax.lines[1].set_ydata([0, gt[t_ind]]); # update labels
axs[0].lines[2].set_visible(show_integrand)
ax_intervals = axs[1].twinx(); ax_intervals.set_visible(False)
def update_plot_intervals():
# Update interval lines
ax_intervals.clear(); ax_intervals.axis('off');
for x in intervals_g:
ax_intervals.axvline(x, color='rwth:red',linestyle='--',lw=1)
try:
toggle_stepwise(stepwise.value)
except: pass
update_plot_intervals()
```
%% Cell type:markdown id: tags:
Verschiebung $t$ kann automatisch abgespielt werden. Eine schrittweise Betrachtung ist ebenfalls möglich.
%% Cell type:code id: tags:
``` python
def update_t_slider(ti):
global interval_cnt
if interval_cnt > len(intervals_gt)-2:
interval_cnt = 0
tmin = intervals_gt[interval_cnt]; tmax = intervals_gt[interval_cnt+1];
t_w.value = tmin + ti/100*(tmax-tmin) # Update float slider
def reset_t_slider(b):
global interval_cnt
play._playing = False
interval_cnt = 0
intslider.value = 0
stepwise.value = False
update_t_slider(0)
def update_stepwise(args):
visible = args['new']
toggle_stepwise(visible)
def toggle_stepwise(visible):
global intervals_gt
ax_intervals.set_visible(visible)
if visible:
intervals_gt = np.hstack([t_w.min, intervals_g, t_w.max ])
else:
intervals_gt = np.array([t_w.min, t_w.max])
# Widget
play = widgets.Play(value=0, min=0, max=100,step=10, description="Press play", show_repeat=False)
stepwise =widgets.Checkbox(value=False, description='Schrittweise')
reset = widgets.Button(description="Reset"); reset.on_click(reset_t_slider);
intslider = widgets.IntSlider(description='Fortschritt') # Dummy slider in integer format, to be mapped to float slider
status = widgets.Label(value='Nothing')
widgets.jslink((play, 'value'), (intslider, 'value')) # Link dummy slider to player
#def update_t_limits(args):
# status.value = str(np.round(intslider.value)) + " " + str(t_w.value) + " " + str(interval_cnt) + " " + str(args['old']) + " " + str(args['new']);
#play.observe(update_t_limits, '_playing')
stepwise.observe(update_stepwise, 'value')
widgets.interactive(update_t_slider, ti = intslider); intslider.layout.display = 'none';
widgets.HBox([play, stepwise, reset, intslider])#, status
```
%% Cell type:markdown id: tags:
Verschiebung $t$ kann automatisch abgespielt werden. Eine schrittweise Betrachtung ist ebenfalls möglich.
%% Cell type:markdown id: tags:
### Aufgaben:
* Bewege den Schieberegler für $t$ und betrachte das entstehende Faltungsintegral. Wie sind die zugehörigen Integralsgrenzen und welche Intervalle (vgl. Notebook zur Faltung) sind zu beobachten?
* Wähle zwei Rechtecke unterschiedlicher Breite aus. Wie sieht das entstehende Signal aus? Wie breit ist es? Was passiert, wenn eins der Rechtecke um $t_0$ verschoben wird?
* Welche Höhe bei $t=0$ hat das Resultat der Faltung $g(t) = \mathrm{rect}\left(\frac{t}{2}\right)\ast \mathrm{rect}\left(\frac{t}{2}\right)$? Überprüfe die Überlegungen mit Hilfe der entsprechenden Funktionen in der Demo.
* Gilt das Kommutativgesetz $s(t) \ast h(t) = h(t) \ast s(t)$?
* Wie sieht das Faltungsergebnis zweier si-Funktionen aus? Wie das Ergebnis zweier Gaußfunktionen?
* Reale Rechteckimpulse weisen nur eine endliche Flankensteilheit auf. Diese können beispielsweise mit $s(t)=\mathrm{rect}(t)*\mathrm{rect}(t/T)$ oder $s(t)=\mathrm{rect}(t)*\Lambda(\frac{t}{T})$ beschrieben werden. Betrachte diese Fälle für $|T|<\frac{1}{2}$. Wie hängen Gesamtdauer und Dauer der Anstiegsflanke von $T$ ab?
%% Cell type:markdown id: tags:
---
This notebook is provided as [Open Educational Resource](https://en.wikipedia.org/wiki/Open_educational_resources) (OER). Feel free to use the notebook for your own purposes. The code is licensed under the [MIT license](https://opensource.org/licenses/MIT).
Please attribute the work as follows:
*Christian Rohlfing, Übungsbeispiele zur Vorlesung "Grundgebiete der Elektrotechnik 3 - Signale und Systeme"*, gehalten von Jens-Rainer Ohm, 2020, Institut für Nachrichtentechnik, RWTH Aachen University.
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