Re: Wanting to take a FFT transform of a irregularly spaced sample

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Robert,
              I ran that code as you suggested. I get this error now -
File "ffttest.py", line 21, in <module>
    signal.lombscargle(minutes,df1.to_numpy().ravel(),freq)
  File
"/usr/local/lib/python3.8/dist-packages/scipy-1.7.1-py3.8-linux-x86_64.egg/scipy/signal/spectral.py",
line 150, in lombscargle
    pgram = _lombscargle(x, y, freqs)
ZeroDivisionError: ()

Any suggestions would be appreciated. Is this an issue I should open on
github by providing the test data ?

Best regards,
Ashwin.



On Tue, Apr 12, 2022 at 6:48 PM Robert Kern <[email protected]> wrote:

> On Tue, Apr 12, 2022 at 3:32 AM ashwin .D <[email protected]> wrote:
>
>> Hi Robert,
>>                   Thanks for your prompt response. I am going to try
>> both. Regarding this answer that you recommended -
>> https://stackoverflow.com/questions/34428886/discrete-fourier-transformation-from-a-list-of-x-y-points/34432195#34432195
>>
>> what would be my angular frequencies from this API -
>> https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.lombscargle.html
>> ?
>>
>> The x and y arguments are straightforward and are available to me from
>> the CSV file. What about the third one ?
>>
>
> That's the angular frequencies at which you want to evaluate the
> periodogram at. In your case (otherwise-regular time series but with
> missing values), I would recommend using the angular frequencies that you
> would have had if you had computed a normal periodogram using the FFT on
> the whole time series, e.g. `np.linspace(0, np.pi/300.0, 8928//2)`
> (assuming your `x` is in seconds). The running time is
> O(len(x)*len(freqs)), though, so that may take a long time. You may want to
> reduce the number of points you sample at first for visualization, then you
> can zoom in at the full frequency resolution to an area of interest if
> there is lots of dead space.
>
> --
> Robert Kern
> _______________________________________________
> SciPy-User mailing list -- [email protected]
> To unsubscribe send an email to [email protected]
> https://mail.python.org/mailman3/lists/scipy-user.python.org/
> Member address: [email protected]
>

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<div dir=3D"ltr">Robert,<div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 I ran that code as you suggested. I get this error now -=C2=A0</div><di=
v>File &quot;ffttest.py&quot;, line 21, in &lt;module&gt;<br>=C2=A0 =C2=A0 =
signal.lombscargle(minutes,df1.to_numpy().ravel(),freq)<br>=C2=A0 File &quo=
t;/usr/local/lib/python3.8/dist-packages/scipy-1.7.1-py3.8-linux-x86_64.egg=
/scipy/signal/spectral.py&quot;, line 150, in lombscargle<br>=C2=A0 =C2=A0 =
pgram =3D _lombscargle(x, y, freqs)<br>ZeroDivisionError: ()<br></div><div>=
<br></div><div>Any suggestions would be appreciated. Is this an issue I sho=
uld open on github by providing the test data ?=C2=A0</div><div><br></div><=
div>Best regards,</div><div>Ashwin.=C2=A0</div><div><br></div><div><br></di=
v></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr=
">On Tue, Apr 12, 2022 at 6:48 PM Robert Kern &lt;<a href=3D"mailto:robert.=
[email protected]">[email protected]</a>&gt; wrote:<br></div><blockquote c=
lass=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px soli=
d rgb(204,204,204);padding-left:1ex"><div dir=3D"ltr"><div dir=3D"ltr">On T=
ue, Apr 12, 2022 at 3:32 AM ashwin .D &lt;<a href=3D"mailto:winash12@gmail.=
com" target=3D"_blank">[email protected]</a>&gt; wrote:<br></div><div clas=
s=3D"gmail_quote"><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px=
 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div di=
r=3D"ltr">Hi Robert,<div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 Thanks for your prompt response. I am going to try both. Rega=
rding this answer that you recommended -=C2=A0<a href=3D"https://stackoverf=
low.com/questions/34428886/discrete-fourier-transformation-from-a-list-of-x=
-y-points/34432195#34432195" target=3D"_blank">https://stackoverflow.com/qu=
estions/34428886/discrete-fourier-transformation-from-a-list-of-x-y-points/=
34432195#34432195</a></div><div><br></div><div>what would be my angular fre=
quencies from this API -=C2=A0<a href=3D"https://docs.scipy.org/doc/scipy/r=
eference/generated/scipy.signal.lombscargle.html" target=3D"_blank">https:/=
/docs.scipy.org/doc/scipy/reference/generated/scipy.signal.lombscargle.html=
</a> ?=C2=A0</div><div><br></div><div>The x and y arguments are straightfor=
ward and are available to me from the CSV file. What about the third one ?=
=C2=A0</div></div></blockquote><div><br></div><div>That&#39;s the angular f=
requencies at which you want to evaluate the periodogram at. In your case (=
otherwise-regular time series but with missing values), I would recommend u=
sing the angular frequencies that you would have had if you had computed a =
normal periodogram using the FFT on the whole time series,=C2=A0e.g. `np.li=
nspace(0, np.pi/300.0, 8928//2)` (assuming your `x` is in seconds). The run=
ning time is O(len(x)*len(freqs)), though, so that may take a long time. Yo=
u may want to reduce the number of points you sample at first for visualiza=
tion, then you can zoom in at the full frequency resolution to an area of i=
nterest if there is lots of dead space.</div></div><div><br></div>-- <br><d=
iv dir=3D"ltr">Robert Kern</div></div>
_______________________________________________<br>
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=3D"_blank">[email protected]</a><br>
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rg" target=3D"_blank">[email protected]</a><br>
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el=3D"noreferrer" target=3D"_blank">https://mail.python.org/mailman3/lists/=
scipy-user.python.org/</a><br>
Member address: <a href=3D"mailto:[email protected]" target=3D"_blank">win=
[email protected]</a><br>
</blockquote></div>

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