Re: [Help-gsl] sign in gsl_sf_legendre_Plm / gsl_sf_legendre_sphPlm

[Denis Davydov]

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 
>