Add a converted MatLab example that was used to figure out the differences between MatLab and matplotlib PSD scaling.

dopplershift · dopplershift · commit 4c17c1fd285d · 2008-12-08T21:16:04.000Z
svn path=/trunk/matplotlib/; revision=6519
diff --git a/examples/pylab_examples/psd_demo3.py b/examples/pylab_examples/psd_demo3.py
@@ -0,0 +1,34 @@
+#This is a ported version of a Matlab example from the signal processing
+#toolbox that showed some difference at one time between Matplotlib's and
+#MatLab's scaling of the PSD.
+
+import numpy as np
+import matplotlib.pyplot as plt
+import matplotlib.mlab as mlab
+
+fs = 1000
+t = np.linspace(0, 0.3, 301)
+A = np.array([2, 8]).reshape(-1, 1)
+f = np.array([150, 140]).reshape(-1, 1)
+xn = (A * np.sin(2 * np.pi * f * t)).sum(axis=0) + 5 * np.random.randn(*t.shape)
+
+yticks = np.arange(-50, 30, 10)
+xticks = np.arange(0,550,100)
+
+plt.subplot(1,2,1)
+plt.psd(xn, NFFT=301, Fs=fs, window=mlab.window_none, pad_to=1024,
+    scale_by_freq=True)
+plt.title('Periodogram PSD Estimate')
+plt.yticks(yticks)
+plt.xticks(xticks)
+plt.grid(True)
+
+plt.subplot(1,2,2)
+plt.psd(xn, NFFT=150, Fs=fs, window=mlab.window_none, noverlap=75, pad_to=512,
+    scale_by_freq=True)
+plt.title('Welch Method PSD Estimate')
+plt.xticks(xticks)
+plt.yticks(yticks)
+plt.grid(True)
+
+plt.show()
