Fourier Analysis & Cross Correlation

[Thomas L. deArth]

Hello,

I am trying to complete my thesis and have run into a bit of a snag and am
desperately hoping to find some assistance. My thesis involves a cross
correlation and Fourier analysis of river stage, discharge and precipitation
data. I, however, am not able to figure out how to run the data in excel.
I have run it on a linex system but was not able to generate the decent
graphs and am now trying run the data on excel but cannot figure out how to
do it. Any assistance is greatly appreciated.

Thank you very much.

 

[Kevin Stecyk]

Thomas,

Are you able to generate your numbers using Linux system? If so, why not
just export the data you want graphed into Excel, and then you can graph
whatever you want?

If you are able, export your Linux system results into a CSV file or TXT
file. Then just import that data into Excel.

I don't do Fourier analysis often, so the only things I could suggest are as
follows:

1) Search Excel postings:
http://www.google.com/advanced_group_search?q=group:*excel

Use Fourier as your search term.

2) Use Google to search for Fourier and Excel.

Hopefully others will jump in as well.

Best regards,
Kevin

 

[Dana DeLouis]

I am not able to figure out how to run the data in excel.

Just out of curiosity, how big is your data? I ask because it may be just
as easy to calculate a Correlation with a custom vba function than with
Excel's Fourier.

The two functions you probably need are IMCONJUGATE and IMPRODUCT. Does
that help?

Personally, the hardest part of Excel's fft is keeping track of the position
of the units digit. I find it best to put the unit number at the top of the
spreadsheet. For a correlation, the other number should be listed in
reverse order. I think this is the hardest part to keep track of. Also,
you need to keep track of the zero's you most likely need to add. Remember,
that the size of the Fourier you need to take is (# of Digits in first + #
of Digits in second), and rounded up to the next 2^n. (Although it is more
correct to subtract 1 from this sum prior to rounding up.)

Anyway, not reversing, and taking the correct size are my two best guesses
for your data not working.