Re: power spectrum/freqs.
- To: mathgroup at smc.vnet.net
- Subject: [mg15338] Re: power spectrum/freqs.
- From: jim leddon <jleddon at cyberramp.net>
- Date: Fri, 8 Jan 1999 04:15:25 -0500
- Sender: owner-wri-mathgroup at wolfram.com
Hi, I have a question regarding calculating the power spectrum and frequencies of a set of intensities values. The data set is a small one(see attached file-Mathematica 3.0). In the attached file, I have calculated and plotted not only a power spectrum but also a power spectrum versus frequencies of a data set of intensity values.I am trying to determine if there are some dominant frequencies or if the power spectrum has a chaotic type behavior shape. set of values and converts these to a frequency domain set of values. It seemed reasonable that once I calculated the FT, I could account for the aliasing by removing the second part of the spectrum and then use the remaining FT values to get the power spectrum which is by definition the absolute value of the the FT(remaining values) multiplied by it's conjugate (remaining values)FT - divided by the square root of the the length of the data list. I then calculated the frequencies based on the FT, although I've noticed that alot of people who have used Mathematica will use the "InverseFourier" function to calculate the power spectrum and frequencies. My question is; in looking at the attached program, am I correct about how to calculate the power spectrum and frequencies? Is it also correct to use the entire FT spectrum times its' conjugate FT to calculate the power spectrum? I also would like to ask if there is a way to use the "Frequencies" function under the "Statistics`DataManipulation`" package in order to calculate the frequencies. I have used this function before, however, there must be some way of ordering the output to correspond with a power spectrum if one wanted to plot both the power spectrum vs. frequencies. Thank you for your time and consideration in reading this email message. I'd look forward to hearing from you if you can help. Regards, Debbie Leddon