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Matplotlib.axes.Axes.psd() in Python
  • Last Updated : 13 Apr, 2020

Matplotlib is a library in Python and it is numerical – mathematical extension for NumPy library. The Axes Class contains most of the figure elements: Axis, Tick, Line2D, Text, Polygon, etc., and sets the coordinate system. And the instances of Axes supports callbacks through a callbacks attribute.

matplotlib.axes.Axes.psd() Function

The Axes.psd() function in axes module of matplotlib library is used to plot the power spectral density.

Syntax: Axes.psd(self, x, NFFT=None, Fs=None, Fc=None, detrend=None, window=None, noverlap=None, pad_to=None, sides=None, scale_by_freq=None, return_line=None, *, data=None, **kwargs)

Parameters: This method accept the following parameters that are described below:

  • x: This parameter is a sequence of data.
  • Fs : This parameter is a scalar. Its default value is 2.
  • window: This parameter take a data segment as an argument and return the windowed version of the segment. Its default value is window_hanning()
  • sides: This parameter specifies which sides of the spectrum to return. This can have following values : ‘default’, ‘onesided’ and ‘twosided’.
  • pad_to : This parameter contains the integer value to which the data segment is padded.
  • NFFT : This parameter contains the number of data points used in each block for the FFT.
  • detrend : This parameter contains the function applied to each segment before fft-ing, designed to remove the mean or linear trend {‘none’, ‘mean’, ‘linear’}.
  • scale_by_freq : This parameter is allows for integration over the returned frequency values.
  • noverlap : This parameter is the number of points of overlap between blocks.
  • Fc : This parameter is the center frequency of x.
  • return_line : This parameter include the line object plotted in the returned values.

Returns: This returns the following:



  • Pxx:This returns the values for the power spectrum P_{xx} before scaling.
  • freqs :This returns the frequencies for the elements in Pxx.
  • line :This returns the line created by this function.

The resultant is (Pxx, freqs, line)

Below examples illustrate the matplotlib.axes.Axes.csd() function in matplotlib.axes:

Example-1:

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# Implementation of matplotlib function
import numpy as np
import matplotlib.pyplot as plt
   
dt = 0.01
t = np.arange(0, 30, dt)
nse1 = np.random.randn(len(t))
   
s1 = 1.5 * np.sin(2 * np.pi * 10 * t) + nse1 + np.cos(np.pi * t)
   
fig, ax1 = plt.subplots()
ax1.psd(s1**2, 512, 1./dt, color ="green")
ax1.set_xlabel('Frequency')
ax1.set_ylabel('PSD(db)')
   
ax1.set_title('matplotlib.axes.Axes.psd() Example')
plt.show()

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Output:

Example-2:

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# Implementation of matplotlib function
import numpy as np
import matplotlib.pyplot as plt
   
dt = 0.01
t = np.arange(0, 30, dt)
nse1 = np.random.randn(len(t))
r = np.exp(-t / 0.05)
   
cnse1 = np.convolve(nse1, r, mode ='same')*dt
   
s1 = np.cos(np.pi * t) + cnse1 + np.sin(2 * np.pi * 10 * t) 
   
fig, [ax1, ax2] = plt.subplots(2, 1)
ax1.plot(t, s1)
ax1.set_xlim(0, 5)
ax1.set_ylabel('value s1')
ax1.grid(True)
   
ax2.psd(s1, 256, 1./dt)
ax2.set_ylabel('PSD(db)')
ax2.set_xlabel('Frequency')
   
ax1.set_title('matplotlib.axes.Axes.psd() Example')
plt.show()

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Output:

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