问Python中的谱图图

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from scipy import signal
import matplotlib.pyplot as plt
import numpy as np

# Define the signal
Fs = 1e4     # Sampling Frequency


# Sin wave with Amplite 1 unit, 50Hz, for duration 0-5 seconds
N1 = (1e5)/2
time1 = np.arange(N1) / float(Fs)          
x1 = 1*np.sin(2*np.pi*50*time1)


# Sin wave with Amplite 0.008 units, 100Hz, for duration 5-10 seconds
time2 = np.arange(N1,2*N1) / float(Fs)
x2 = 0.008*np.sin(2*np.pi*100*time2)


# Concatenate above two waves
T    =np.concatenate((time1,time2))
Y    =np.concatenate((x1,x2))



# Plot the waves
plt.plot(T , Y)
plt.title('Time Data')
plt.ylabel('Amplitude')
plt.xlabel('Time [sec]')
plt.show()


# spectrogram 
freq_axis, time_axis, Sxx = signal.spectrogram(Y, Fs)


# Plot the spectrogram 
plt.pcolormesh(time_axis, freq_axis, Sxx)
plt.title('Spectrogram')
plt.ylabel('Frequency [Hz]')
plt.xlabel('Time [sec]')
plt.xlim(0,10)
plt.ylim(0,200)
plt.show()