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Re: FFT phase? [message #82911 is a reply to message #82909]

Thu, 24 January 2013 22:49

xqinshan
Messages: 21
Registered: November 2008

Junior Member

Thanks. I have known the reason. What I use is like x= 2*!dpi*2*dindgen(25)/16, so the amplitude and phase are not so accurate.

在 2013年1月25日星期五UTC+8上午10时11分30秒，Craig Markwardt写道：
> On Thursday, January 24, 2013 12:28:02 PM UTC-5, xqin...@gmail.com wrote:
>
>> Hi,
>
>>
>
>>
>
>>
>
>> just use FFT(y). For example, y=A*cos(x+B), C=fft(y). I think atan(C,/phase) should equal to B, but the return reslut is not. How to obtain A and B from complex C?
>
>
>
> It is correct. Example:
>
> x = 2*!dpi*2*dindgen(16)/16 ;; Angle in radians
>
> y = 0.7*cos(x + 1.6000)
>
> c = fft(y,-1)
>
> print, atan(c[2],/phase)
>
> ==> 1.6000
>
>
>
> Craig

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[Message index]

		Re: FFT phase? By: Craig Markwardt on Fri, 25 January 2013 13:48
		Re: FFT phase? By: Yngvar Larsen on Fri, 25 January 2013 05:18
		Re: FFT phase? By: xqinshan on Thu, 24 January 2013 22:49
		Re: FFT phase? By: Craig Markwardt on Thu, 24 January 2013 18:11

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