Re: [Matplotlib-users] psd question...

[3togo <fre...@gm...>]

#This program below do reveal that mlab.psd and pyplot.psd are different
http://www.nabble.com/file/p24713274/psd_testpng.png psd_testpng.png 
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.mlab as mlab
dt = np.pi / 100.
fs = 1. / dt
t = np.arange(0, 8, dt)
y = 10. * np.sin(2 * np.pi * 4 * t) + 5. * np.sin(2 * np.pi * 4.25 * t)
y = y + np.random.randn(*t.shape)
print "t=",t
print "y=",y
print "fs=",fs
#Plot the raw time series
fig = plt.figure()
fig.subplots_adjust(hspace=0.6, wspace=0.5)
#
ax = fig.add_subplot(3, 1, 1)
plt.title('Data')
ax.plot(t,y)

ax = fig.add_subplot(3, 1, 2)
plt.title('psd using pyplot')
ax.psd(y,Fs=fs,scale_by_freq=False)

ax = fig.add_subplot(3, 1, 3)
plt.title('psd using mlab')
x,y=mlab.psd(y,Fs=fs,scale_by_freq=False)
ax.plot(y,x)
plt.show()


Lewis, Ambrose J. wrote:
> 
> Hi All:
> 
> I'm trying to use the matplotlib psd function to plot some data.  The
> result from MATLAB's pWelch function looks vastly different.
> 
> Any suggestions/recommendations would be greatly appreciated!
> 
> THANXS
> 
> amb
> 
>  
> 
> Here is the MATLAB code:
> 
> Fs = 13e6;
> 
> fid = fopen('C:\asp\roseRT\ics_output.bin', 'r', 'ieee-le');
> 
> s = fread(fid, [2, Inf], 'int32');
> 
> fclose(fid);
> 
> z = complex(s(2,:), s(1,:));
> 
> pwelch(z, [], [], [], Fs)
> 
>  
> 
> And here is the (hypothetically) equivalent Python/matplotlib code:
> 
>                 datatype = np.complex64
> 
>                 fd = open(self.filename, 'rb')
> 
>                 read_data = np.fromfile(file=fd, dtype=datatype)
> 
>                 Pxx,freqs = psd(read_data,Fs=13000000) 
> 
>                 self.axes.plot(freqs, 10*log10(Pxx) ) 
> 
>                 self.canvas.draw()
> 
>  
> 
> Ambrose Lewis
> 
> SAIC
> 
> 4001 N Fairfax Drive, Suite 400
> 
> Arlington, VA 22203
> 
> 703.558.2786
> 
> amb...@sa... 
> 
>  
> 
> 
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