🚀 go-pugleaf

In article <POPAT.92Aug6115014@image.mit.edu>, popat@image.mit.edu (Kris
Popat) writes:
>
>In article <ALIEN.92Aug6090438@vulcan.essex.ac.uk>, alien@essex.ac.uk
>("Adrian F Clark") writes
>
>> that it can be decomposed into a series of 1-D FFTs.  In other words,
>> you FFT along all the rows, then FFT down all the columns.  (This is
>> not, however a very efficient way to do it!) [...]
>
>Actually, row-column decomposition IS a fairly efficient way to
>compute a 2-D DFT.  Slightly faster methods exist (e.g., vector-radix
>FFTs), but the speed-up over row-column decomposition is usually
>small, and may not be worth the extra difficulty in programming
>(considerable).  Row-column decomposition gets you down to the right
>order of complexity.

Well I have only one data point, but I found that on an RS6000 using IBMs
ESSL library, a large 3D FFT (say 60x60x60) runs about twice as fast as
splitting it along three dimensions and do each ray. Presumably the hit
isn't quite as bad in 2D. I imagine whatever ESSL uses for the 3D FFT
directly is the best known- it's a rather impressive library.

Maynard Handley