Re: power spectrum

*To*: mathgroup at smc.vnet.net*Subject*: [mg52742] Re: [mg52695] power spectrum*From*: Sseziwa Mukasa <mukasa at jeol.com>*Date*: Sat, 11 Dec 2004 05:22:05 -0500 (EST)*References*: <200412100123.UAA18915@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On Dec 9, 2004, at 8:23 PM, George Szpiro wrote: > If I have a string of data - let us say a time series of 200 > observations - > how can I find the power spectrum? I did Fourier[list] but have no > idea what > the output means. > > Thank you for any help (please to my email address: > george at netvision.net.il) > If your data is real valued ListPlot[Abs[Fourier[list]][[Range[Quotient[Length[list],2]+1]]],PlotJoi ned->True] will give you the power spectrum from frequencies 0 to half your sample rate. For complex valued observations ListPlot[Abs[RotateRight[Fourier[list],Quotient[Length[list],2]]],PlotJo ined->True] will give you the power spectrum from -1/2*sample rate to 1/2*sample rate - 1/(Length[list] * sample rate). As for what it all means, section 13.4 of Numerical Recipes (http://lib-www.lanl.gov/numerical/index.html) explains power spectra. Regards, Ssezi

**References**:**power spectrum***From:*George Szpiro <george@netvision.net.il>