I want to transform data to DFT and reconstruct it with IDFT
So basically I’m trying to do something like in this Excel tutorial:
There’s a =fourier() function in Calc, but It’s kinda different from what’s on Excel. Can anyone explain how to use it?
I also want to extend the IDFT’ed function outside data spectrum
Given that it appeared as resolution of tdf#74664, which explicitly asked for "Fourier Analysis" function from Data Analysis Toolkit, it’s unexpected and should be a bug - but you never explained what specifically is “kinda different”.
Some documentation is, as expected, in the help: FOURIER function, Fourier Analysis.
Inputs seems kinda different. Excel has these “Component” index input and “N” number of observations. Calc has everything merged into one function and it is missing some components I mentioned. I just don’t know what should I input into =fourier() function to make the results similar to one in tutorial
Example file with finished calculations would be helpful
The video that you linked to in your question has this pinned at the top of the comments:
The DFT and IDFT are part of NumXL. NumXL is an Excel Add-in for time series analysis. Once NumXL is installed on your system, it will add scores of functions (e.g. DFT) to Excel. To download a 30-day free trial, visit our main website.
So the DFT/IDFT functions are not part of Excel, and even not part of its “Analysis ToolPack” that is a separate download for Excel from MS; but some third party tool.
Hope someone helps you getting some sort of formula to get the needed results; but actually, “I want results like in a tutorial for a closed-source third-party add-on” is a bad question; more appropriate would be “I need this math formula be implemented as Calc formula”.
Unfortunately the latest help version Mike linked to has no media files; if in the URL you replace /latest/ with /7.4/ then under the data table the Open file with example: has an actually working sample file linked: FOURIER function .
yeah - that was tdf#150162
Hello All,
This is my first reply here, and for the sake of full transparency, I do work for NumXL.
I found this discussion thread, and I like to add one comment: on our support site, we posted detailed formulas for reversing the DFT (i.e., IDFT) by using a series of cosine functions.
(secretly hoping this comment to signify an interest from the add-in developer to create one for LibreOffice 
)
I sure hope NumXL can support LibreOffice one day, at least, on the Windows platform. I will take this suggestion back to our team, and see how we can prioritize it.