search

David-Berghaus / q-expansion

Code to compute modular forms on noncongruence subgroups
GNU General Public License v3.0
0 stars 0 forks source link

Handle case when there is no expression linear in u #96

Open David-Berghaus opened 1 year ago

David-Berghaus commented 1 year ago

It happens for some rare cases that the Belyi map (for genus zero subgroups) or the Fourier expansion of the weight two cuspform (for g>0 cases) contains no expressions that are linear in u.

The program therefore cannot determine a closed-form expression for u and terminates. While it is often possible to find u "by hand" and then "feed it" to the program, it would be nice to solve these cases automatically.

David-Berghaus commented 1 year ago

An attempt was made in https://github.com/David-Berghaus/q-expansion/commit/8e63cf7fc03a66280cb4cc5a160a40994904af41 to find u from an expression quadratic in u, which is however not guaranteed to always succeed.