# Function problem **URL:** \ **Category:** General Discussion\ **Created:** [December 21, 2022, 10:46am UTC](https://community.freefem.org/t/function-problem/2197 "2022-12-21T10:46:57Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![kuma](https://avatars.discourse-cdn.com/v4/letter/k/a587f6/32.png) [@kuma](https://community.freefem.org/u/kuma)\ **Post date:** [December 21, 2022, 10:46am UTC](https://community.freefem.org/t/function-problem/2197/1 "2022-12-21T10:46:57Z")
How to express jacobian elliptic function in ff. ![图片](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/0/0872a7e9e165af111d7c95acb9993a0c84fde7e6.png) sn-1 is the inverse function of sn.k is a constant and I need to express the function y=snx. Thank you so much for any help. ---
**Author:** ![julienG](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/julieng/32/222_2.png) [@julienG](https://community.freefem.org/u/julienG)\ **Post date:** [December 21, 2022, 4:02pm UTC](https://community.freefem.org/t/function-problem/2197/2 "2022-12-21T16:02:29Z")
The Jacobian Elliptic functions are defined in [GSL](https://www.gnu.org/software/gsl/doc/html/specfunc.html#elliptic-functions-jacobi) and gsl is interfaced in freefem via the [GSL plugin](https://doc.freefem.org/documentation/plugins.html#gsl). However, if you check the `gsl.idp` plugin, you can see that `gsl_sf_elljac_e` (in the freefem language it’s `gslsfelljace`) is not listed there. So this means it is not added yet. I think this should be easily added, in the file `plugin/seq/ff_gsl_awk.hpp`. (I cannot do more right now) I hope this helps ---
**Author:** ![kuma](https://avatars.discourse-cdn.com/v4/letter/k/a587f6/32.png) [@kuma](https://community.freefem.org/u/kuma)\ **Post date:** [December 22, 2022, 2:47am UTC](https://community.freefem.org/t/function-problem/2197/3 "2022-12-22T02:47:58Z")
Thank you for your response! Maybe I should try another way.