lowrank/rte

convolution product

lowrank opened this issue · 2 comments

The Henyey Greenstein function is actually a conv-prod.

In 2d, FFT suffices to get it in O(nlog n) time, supposing there are n angles.
in 3d, it will consume, O(n^3 (log n)^2) time, supposing there are both n angles in the Euler angles.

which is superior than 2d's O(n^2) and 3d's O(n^4). But only approximately just one order better.

It seems not very necessary due to the angular space's discretization has very small number of angles. I guess there is not obvious difference for small cases. But it is always good to have one.

done by 376ecf1