Opened 6 years ago
Last modified 5 years ago
#21798 new enhancement
Implement degeneracy maps to make JH(22, [-1]).decomposition() work
Reported by: | pbruin | Owned by: | |
---|---|---|---|
Priority: | major | Milestone: | sage-7.5 |
Component: | modular forms | Keywords: | |
Cc: | mderickx | Merged in: | |
Authors: | Reviewers: | ||
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | #21927 | Stopgaps: |
Description (last modified by )
In SageMath 7.5.rc0:
sage: JH(22, [-1]).decomposition() Traceback (most recent call last): ... NotImplementedError:
The thing that is not implemented is a degeneracy map between spaces of modular symbols.
See also #21799.
Change History (7)
comment:1 Changed 6 years ago by
- Cc mderickx added
- Description modified (diff)
comment:2 Changed 6 years ago by
comment:3 Changed 5 years ago by
It seems the following is a more immediate example:
sage: ModularSymbols(GammaH(11, [-1]), 2).modular_symbols_of_level(22) Traceback (most recent call last): ... ValueError: N (=22) should be a factor of the level of this space (=11)
This does work when replacing GammaH(11, [-1])
by Gamma1(11)
or Gamma0(11)
.
comment:4 Changed 5 years ago by
The above error is apparently deliberate, according to the following comment in the method sage.modular.modsym.ambient.ModularSymbolsAmbient_wtk_gamma_h.modular_symbols_of_level
:
# We deliberately don't allow N to be a multiple of the level here, # because there are many possibilities for what H could be at the # higher level (and we don't implement the degeneracy raising maps # anyway)
A canonical choice for the H
at higher level N
is to take the inverse image of H
in (Z/NZ)^{×}. However, we then still have to implement the degeneracy maps. Doing this will require implementing the function sage.modular.arithgroup.congroup.degeneracy_coset_representatives_gamma_h
and the method sage.modular.modsym.ambient.ModularSymbolsAmbient_wtk_gamma_h._degeneracy_raising_matrix_1
.
comment:5 Changed 5 years ago by
- Dependencies set to #21927
After #21927, the error occurs slightly later on, and a NotImplementedError
is raised instead of a ValueError
.
comment:6 Changed 5 years ago by
- Description modified (diff)
- Summary changed from JH(22, [-1]).decomposition() raises ValueError to Implement degeneracy maps to make JH(22, [-1]).decomposition() work
- Type changed from defect to enhancement
comment:7 Changed 5 years ago by
A more immediate example:
sage: M = ModularSymbols(GammaH(22, [-1]), 2) sage: N = ModularSymbols(GammaH(11, [-1]), 2) sage: N.degeneracy_map(M, 1) Traceback (most recent call last): ... NotImplementedError:
The funny spacing in the error message should also be fixed.