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 <davyd...@gmail.com> 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 >
