jdupuy / dj_fft Goto Github PK

Nothing big; just noticed that the enum class, specifying the direction in which to calculate the FFT, is outdated in the usage example in the README file. It should be dj::fft_dir::DIR_FWD and not dj::fft_dir::FFT_FWD.

Thanks for the repo - really useful 👍

Hello,

I'm struggling here with the algorithm.

I'm comparing the result of R's fft and another fft's I found on the internet and the result is not the same as dj-fft.

For example:

complex_vector = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}

fft(complex_vector) returns:

 [1] 11.0625353+0.0000073i -1.2694808-1.8365898i -0.8289607-1.0336070i -0.6982133-0.6797898i -0.6415854-0.4676793i -0.6127618-0.3175757i -0.5972594-0.1986772i
 [8] -0.5894584-0.0958635i -0.5870695-0.0000038i -0.5894589+0.0958638i -0.5972596+0.1986813i -0.6127663+0.3175770i -0.6415888+0.4676792i -0.6982226+0.6797901i
[15] -0.8289628+1.0336033i -1.2694881+1.8365879i

but the correct should be:

 [1] 136+ 0.000000i  -8+40.218716i  -8+19.313708i  -8+11.972846i  -8+ 8.000000i  -8+ 5.345429i  -8+ 3.313708i  -8+ 1.591299i  -8+ 0.000000i  -8- 1.591299i  -8- 3.313708i
[12]  -8- 5.345429i  -8- 8.000000i  -8-11.972846i  -8-19.313708i  -8-40.218716i

I'm trying to find where is the problem meanwhile.

Thank you.

Public domain is a difficult concept to work around when it comes to OSS licensing and incorporating code into projects. Furthermore, dj_fft does not declare this formally using a document like CC0, meaning a few things:

• The definition of 'public domain' rests in the jurisdiction of the licensee or user
• Public domain software may be able to be revoked in some cases and jurisdictions.
• The status of the software being public domain is almost certainly illegitimate with such a small clause stating so (that does not explicitly waive copyright)
• You may be liable for your software that you release in public domain (ie. if your compute shader FFT implementation contributes to damaging graphics hardware)

Additionally, the incorporeality of public domain software in OSS projects encounters a problem with sub-licensing, where this is a gray area (the CC0 license is more explicit in this case and probably won't cause an issue, but your declaration of public domain makes this a problem).

For more information, see this SE post, and GNU licensing notes on informal licenses.

Assuming you wished to grant full rights to your users, I suggest:

• Releasing the code under MIT
• Or, dual licensing the code under CC0 and MIT if you have a good reason to prefer the code released in the public domain.

However, if want to keep your software available to the public including modifications to it, use the GPLv3.

Obligatory: I am not a lawyer and this is not formal legal advice