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Re: Complications with variance using FFTs [message #40126 is a reply to message #40125]

Wed, 21 July 2004 10:53

olde_english33
Messages: 7
Registered: June 2004

Junior Member

Craig Markwardt <craigmnet@REMOVEcow.physics.wisc.edu> wrote in message news:<onllheeqc8.fsf@cow.physics.wisc.edu>...
> olde_english33@hotmail.com (Eric) writes:
>>
>> Hello. First, I don't understand what you mean by "multiplied by
>> exp(-phi)? Secondly, consider the following code instead:
>
> I mean, that for a real signal, the Fourier components at negative
> frequencies are the complex conjugate of those at positive
> frequencies. Thus, EXP(IMAG*PHI) at positive frequencies becomes
> EXP(-IMAG*PHI) at negative frequencies, for arbitrary PHI. Since you
> are not changing to the complex conjugate at negative frequencies, I
> think that's where your problem lies.
>
>> Now I think all the code snipets are related correctly. I checked the
>> the average variance of all the xf1[*,i] was equal to
>> sum(avgspec1)/31.0 and that the average variance of xf2[*,i] was equal
>> to sum(avgspec2)/31.0. This check held. It works if I don't throw in
>> the symmetric random phase exp(e). Does this phase throw off the
>> variance? Is there any way to account for inputting this random
>> phase?
>
> Well, it's still worth investigating the original questions I posed...
>
> Craig

From what I can gather from my program, the positive frequencies are
those from 1:15. Then the frequencies from 16:30 are the complex
conjugates of the frequencies from 15:1. Therefore, I thinkt that IDL
is already accounting for the complex conjugate in the negative
frequencies, unless I am missing something.

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[Message index]

		Re: Complications with variance using FFTs By: olde_english33 on Thu, 22 July 2004 10:06
		Re: Complications with variance using FFTs By: Craig Markwardt on Wed, 21 July 2004 11:30
		Re: Complications with variance using FFTs By: olde_english33 on Wed, 21 July 2004 10:53
		Re: Complications with variance using FFTs By: Craig Markwardt on Tue, 20 July 2004 06:54
		Re: Complications with variance using FFTs By: olde_english33 on Mon, 19 July 2004 09:19
		Re: Complications with variance using FFTs By: Craig Markwardt on Fri, 16 July 2004 14:21

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