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## [Help-gsl] spherical harmonics for m<0 (m=-l)

 From: Drew Parsons Subject: [Help-gsl] spherical harmonics for m<0 (m=-l) Date: Fri, 23 Sep 2005 12:31:36 +1000

I'm working with spherical harmonics, calculated a value for each l
separately by putting together a sum over m of Y_l^m (averaging the
value of the spherical harmonic over a number of neighbouring points in
space) , as in

\sum_{m=-l}^{l}  < Y_l^m (\theta, \phi ) >

To help get this done GSL offers me gsl_sf_legendre_sphPlm( l, m, x ),
but the function only accepts m >= 0.

What is the best way to proceed to also count the cases where m < 0 ?

Drew Parsons