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Re: [Help-gsl] sign in gsl_sf_legendre_Plm / gsl_sf_legendre_sphPlm
From: |
Denis Davydov |
Subject: |
Re: [Help-gsl] sign in gsl_sf_legendre_Plm / gsl_sf_legendre_sphPlm |
Date: |
Thu, 30 Oct 2014 10:23:06 +0100 |
Never mind, the issue is solved.
It turned out that the pre-factor (-1)^m is included in the definition of
Legendre polynomials, even though “m” is required to be positive in
gsl_sf_legendre_Plm .
Perhaps this fact could be mentioned in the documentation to avoid confusion.
Kind regards,
Denis
> On 29 Oct 2014, at 19:33, Denis Davydov <address@hidden> wrote:
>
> Dear all,
>
> I am trying to use the associated Legendre polynomials,
> but I am confused about the sign.
> I would expect P_1^1(cos(phi)) = sin(phi) > 0 and
> therefore to have the normalised polynomial also positive.
> However, it seems that there is a (-1)^m multiplier
> compared to the expression I see in several books.
> Could someone please clarify this issue for me?
>
> Kind regards,
> Denis
>