On the subject of FFT and other transforms, I went to take another look at the JTransforms code, which is AFAIK the premiere transforms package for Java (even outperforming FFTW) and which I myself use over Commons.
It is now on GitHub so it was easy to browse the source code. It is in pure Java and even has a commons-3 dependency (on FastMath). Other than that, from the code I looked at, it is only dependent on another package by the same author, JLargeArrays. This must be an issue around commons from time to time. The reasonable choice for a Java user would be JTransforms. It would be needless time and effort to reinvent the wheel, this author has been refining the package for 10+ years. On the other hand we will need an FFT going forward, and it is part of the commons mission to be self-contained. JTransforms is open source so it could potentially be adapted for sigproc and numbers. For example, it doesn't take Complex arrays but only double arrays that alternate real and imaginary, which are awkward to deal with -- that is why I wrote methods, now in ComplexUtils, to deal with it. But there's no question that overwhelmingly such an adaptation would remain the same as the current library. Is there a recommended way to proceed?
