I'm trying to implement a simple FHT on .NET platform myself. I follow this document: Optimized fast Hartley transform for the MC68000 with applications in image processing.
In the page 20th, equation (20):
H(k) = He(k) + [Ho(k)cos(2πk/N) + Ho(N/2-k)sin(2πk/N)]
H(k+N/2) = He(k) - [Ho(k)cos(2πk/N) + Ho(N/2-k)sin(2πk/N)]
He(k) is the N/2 point DHT of the even indexed elements of H(k) and
Ho(k) is the N/2 point DHT of the odd indexed elements of H(k)
$k$ is zero index, so where is the item $N/2$ if $N/2$ is the length? I know I must have misunderstood something, but I realy don't know what exactly the Ho and He are. I have succeeded implement the FFT equation (in the page 17th). But the FHT, I can not.
Can somebody please help me explain the above equation details?