What version of mpl are you using? These functions got a lot of work between 1.3 and 1.4.
I also suspects that there is a normalization issue going on with power vs power density.
Tom
···
On Tue, Dec 16, 2014, 22:28 xkryptor <xkryptor@…287…> wrote:
Hi all,
I tried calculating the power spectral density using matplotlib mlab function psd (). I plotted using two methods:
- At first I plot it directly using plt.psd (red line in plot)
- Then I output the values from psd() to variables and plotting the
variables (blue line in plot)
The code I used:
power, freqs = plt.psd(P * 100000, len(P), Fs = 1 / dt, scale_by_freq=0)
plt.psd(P * 100000, len(P), 1 / dt, scale_by_freq=0)
plt.plot(freqs, power)
But the plots are different, I expected it to be coincident. From where does the discrepancy arise?
![Inline image 1]()
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What version of mpl are you using? These functions got a lot of work
between 1.3 and 1.4.
Tom,
Sorry, I answered only in his parallel github issue. matplotlib power spectral density (PSD) value discrepancy · Issue #3927 · matplotlib/matplotlib · GitHub. I'm closing it now. The upshot is that psd returns the power but plots it in db.
Eric
···
On 2014/12/17, 5:37 AM, Thomas Caswell wrote:
I also suspects that there is a normalization issue going on with power
vs power density.
Tom
On Tue, Dec 16, 2014, 22:28 xkryptor <xkryptor@...287... > <mailto:xkryptor@…287…>> wrote:
Hi all,
I tried calculating the power spectral density using matplotlib
mlab function psd (). I plotted using two methods:
1. At first I plot it directly using plt.psd (red line in plot)
2. Then I output the values from psd() to variables and plotting the
variables (blue line in plot)
The code I used:
power, freqs = plt.psd(P * 100000, len(P), Fs = 1 / dt, scale_by_freq=0)
plt.psd(P * 100000, len(P), 1 / dt, scale_by_freq=0)
plt.plot(freqs, power)
But the plots are different, I expected it to be coincident. From
where does the discrepancy arise?
Inline image 1
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