Re: fourier transform

*To*: mathgroup at smc.vnet.net*Subject*: [mg61237] Re: [mg61203] fourier transform*From*: Pratik Desai <pdesai1 at umbc.edu>*Date*: Thu, 13 Oct 2005 01:39:45 -0400 (EDT)*References*: <200510120543.BAA09326@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

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

**References**:**fourier transform***From:*Masrur Hossain <Lessjunk@yahoo.com>