I am a total beginner but I want to post that a lot.
auto autoCorrelation(R)(R range)
if (isRandomAccessRange!R)
{
import std.numeric : fft, inverseFft;
import std.range : chain, repeat, zip, dropBack;
import std.algorithm : map;
import std.complex;
auto residual = residualPowerOf2(range.length);
auto fftResult = range.chain(repeat(0, residual)).fft();
auto autoCorrResult = fftResult.zip(fftResult.map!(a =>
a.conj())).
map!( a=> a[0] * a[1] ).
inverseFft().
dropBack(residual).
map!( a => a.re );
return autoCorrResult;
}
I implemented auto correlation in C++ before which is I believe
2~3 time bigger(also I needed to compile fftw, lapack etc.. ) :
https://forum.kde.org/viewtopic.php?f=74&t=118619 .
That was the moment I feel in love with D.