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MathGroup Archive 2005

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Re: fourier transform

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61238] Re: [mg61203] fourier transform
  • From: Pratik Desai <pdesai1 at umbc.edu>
  • Date: Thu, 13 Oct 2005 01:39:46 -0400 (EDT)
  • References: <200510120543.BAA09326@smc.vnet.net> <434DCA7B.3070004@umbc.edu>
  • Sender: owner-wri-mathgroup at wolfram.com

Pratik Desai wrote:

> Masrur Hossain wrote:
>
>> Hi folks
>>           I have a list of pairs of numbers like
>>
>>  {{1.2, 3.4}, {2.2, 3.6}............}
>> The first part is time and second part is amplitude.
>>
>> when I do the fourier transform by using
>> Fourier[list]
>>
>> it gives me list of complex numbers but I expect real numbers
>> (i.e . amplitude versus frequency)
>>  
>>
> It should give you complex numbers, that is the whole idea of Fourier 
> Transform (  I think  :-\ )
> You can find the amplitude(frequency domain Frequency Response 
> Function) simply by taking the absolute value and plotting it with 
> respect to the number of points, and obviously the  phase is given  by 
> taking Arg. I may be wrong about this but I don't think the way you 
> have constructed your input list will work, the best way is to do is 
> to construct your list with only amplitudes with a suitable time step. 
> To gurantee good results the number of  points  should be something 
> like  2^n ;-)       .....256, 512, 1024 etc.
>
>>
>> Any help appreciated.
>>
>> thanks
>>  
>>
> Hope this helps
>
>
> Pratik  .
>
You can find more information on this in the Mathematica Book 3.8.4

Just type 3.8.4 in help browser in Mathematica



-- 
Pratik Desai
Graduate Student
UMBC
Department of Mechanical Engineering
Phone: 410 455 8134



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