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• 如何在Python中绘制幅值突变的正弦波？

# 如何在Python中绘制幅值突变的正弦波？ [英] How to plot sine wave in Python with sudden amplitude change?

### 问题描述

``````import numpy as np
import matplotlib.pyplot as plotter
from scipy import signal
# How many time points are needed i,e., Sampling Frequency
samplingFrequency   = 1500
# At what intervals time points are sampled
samplingInterval       = 1 / samplingFrequency;
# Begin time period of the signals
beginTime           = 0;
# End time period of the signals
endTime             = 0.3;
# Frequency of the signals
signal1Frequency     = 50;
#Time points
time  = np.arange(beginTime, endTime, samplingInterval);
phase = 180
pi = np.pi
phi = phase*pi/180
# Create two waves- sine and square
amplitude1 = np.sin(2*np.pi*signal1Frequency*time)

amplitude2 = signal.square(2 * np.pi * 50 * time+ phi )
figure, axis = plotter.subplots(1, 1)

if (time >0.2):
amplitude = 3*amplitude1
plotter.plot(time, amplitude)
plotter.title('test')
plotter.show()
``````

### 推荐答案

``````import matplotlib.pyplot as plt
import math

# ------------------------------------------------------------------------
# uses the list amplitude_changes to get the amplitude for time t
def get_amplitude(t):
for amplitude_change in amplitude_changes:
if t >= amplitude_change['t']:
amplitude = amplitude_change['amplitude']

return amplitude

# --------------------------------------------------------------------------
def y_func(time, period_time, amplitude):
return amplitude * math.sin((time / period_time) * 2 * math.pi)

# --------------------------------------------------------------------------

t_values = []
amplitude_values = []

signal1Frequency = 50
period_time = 1 / signal1Frequency
sampling_frequency = 1500

delta_t = 1 / sampling_frequency

amplitude_changes = [
{'t': 0, 'amplitude': 1},
{'t': period_time * 0.9, 'amplitude': 1.5},
{'t': period_time * 0.95, 'amplitude': 1},
{'t': period_time * 1.2, 'amplitude': 0.8},
{'t': period_time * 1.25, 'amplitude': 1},
]

max_t = period_time * 3                     # plot 3 periods
t = 0
while t <= max_t:
t_values.append(t)
amplitude = get_amplitude(t)
amplitude_values.append(y_func(t, period_time, amplitude))
t += delta_t

plt.plot(t_values, amplitude_values)
plt.title(f'f = {signal1Frequency} Hz (T = {period_time}) - Sampling frequency = {sampling_frequency} Hz')
plt.show()
``````