Problem with Hecke eigenvalues with the same index as the level

[fredstro]

It seems to be a problem to compute Hecke eigenvalues for Modular Symbol subspaces at integers dividing the level N unless the eigenvalue for the Hecke operator at N is computed first.
I have verified this problem for sage versions between 5.8 and 5.12.beta.

Example

sage: M=ModularSymbols(5,6,sign=1)
sage: S=M.decomposition()
sage: f=S[0]
sage: f.eigenvalue(10)
IndexError                                Traceback (most recent call last)
...
IndexError: n must be a positive integer
sage: f.eigenvalue(5)
25
sage: f.eigenvalue(10)
50

Component: modular forms

Author: Alex Ghitza

Branch/Commit: 56341a3

Reviewer: Peter Bruin

Issue created by migration from https://trac.sagemath.org/ticket/15201

[aghitza]

comment:3

The code used the recursive formula for the Hecke eigenvalues of p-power index without implementing the base case. This is fixed in the attached branch.

[aghitza]

Branch: u/AlexGhitza/ticket/15201

[aghitza]

Author: Alex Ghitza

[aghitza]

Commit: 56341a3

[aghitza]

New commits:

56341a3

fix Hecke eigenvalues recurrence

[pjbruin]

Reviewer: Peter Bruin

[vbraun]

Changed branch from u/AlexGhitza/ticket/15201 to 56341a3