[Algorithms] Pick dominant light from sh coeffs

[Dan T. <dan...@gm...>]

I have 9 red, 9 green and 9 blue sh coefficients (packed using the method
in appendix 10 of http://www.ppsloan.org/publications/StupidSH36.pdf).

I want to pick a single dominant light to use for specular. How would I go
about efficiently extracting the direction and color of that light from the
coefficients?

Looks like I need to calculate the "optimal linear direction" which is
supposedly in this paper
http://research.microsoft.com/en-us/um/people/johnsny/papers/ldprt.pdf, however
I can't see it. Worse still, if it is in there, it is probably an integral
that I will struggle to turn into code!

Thanks

Dan