[CIG-MC] CitcomS Legendre polynomial normalization

Magali Billen mibillen at ucdavis.edu
Wed Mar 3 17:26:21 PST 2010

Hello Shijie,

Yes, its the factors in the recursion relationship that we were  
surprised to find, as the rest the
recursion relationship steps are the same as that in Numerical  
recipes...I'm glad to know that this
is stable for large L as we'll be going up to about L=360. Any chance  
that there's a reference
for the recursion relationship (or maybe point us in the right  
direction, we've looked up several others
and haven't found the same thing)? No hurry, but it seems like this is  
a good thing to have reference for general
CitcomS background information too.

Thanks for answering our e-mail so quickly,

On Mar 3, 2010, at 5:13 PM, Shijie Zhong wrote:

> You are right that the recursion relation for the Legendre  
> polynomials used in
> CitcomS is different from the standard in Numerical Recipes by  
> Press. The
> standard one in Numerical Recipes blows up for spherical harmonic  
> degree l >
> 20 or something, even with double precision computation. I re- 
> derived a
> recursion relation in 1997 that is stable for nearly all l's and is  
> used in CitcomS.

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