
From:  John Gehman 
Subject:  Re: [Helpgsl] spherical harmonics for m<0 (m=l) 
Date:  Wed, 28 Sep 2005 09:45:44 +1000 
I hesitated to reply with this earlier, as I presumed that mucking into the functions with this degree of detail to solve the problem defeats the purpose of a simple gsl function, but in light of Brian's reply, perhaps it helps ... ?
Cheers john On 28/09/2005, at 2:44 AM, Brian Gough wrote:
Drew Parsons writes: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 thevalue of the spherical harmonic over a number of neighbouring points inspace) , 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 ?I think there is a relationship between +m and m (Abramowitz &Stegun 8.2.5) If you are computing multiple values you'll want to use the sphPlm_array function for efficiency. I'm not sure why the original function is restricted to m>=0, maybe there was a reason for that.  Brian Gough Network Theory Ltd, Publishing Free Software Manuals  http://www.networktheory.co.uk/ _______________________________________________ Helpgsl mailing list address@hidden http://lists.gnu.org/mailman/listinfo/helpgsl
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