[Help-gsl] Incomplete elliptic integral (Legendre) (quasi-)periodicity issue

[Lionel Barnett]

Greetings,

It appears that the function gsl_sf_ellint_E(phi,m) is periodic with
period 2\pi. However, E(\phi|m), even under the definition at:

http://www.gnu.org/software/gsl/manual/html_node/Definition-of-Legendre-Forms.html#Definition-of-Legendre-Forms

is actually *quasi*-periodic, satisfying the relation:

E(\phi+n\pi,m) = 2n E(m) + E(\phi,m)

Now I can use this relationship to calculate the correct value of
E(\phi,m) for larger \phi ... except for \pi/2 < \phi < \pi

Any ideas how to do this?

--
Lionel B