Opened 12 years ago

Closed 11 years ago

# Gamma0 equivalence function for number field cusps returns wrong transformation matrix

Reported by: Owned by: mtaranes craigcitro major sage-4.6.1 modular forms number field cusps cremona sage-4.6.1.rc0 Maite Aranes David Loeffler N/A

### Description

The transformation matrix returned by 'is_Gamma0_equivalent' for number field cusps is not in Gamma0(N). My fault (this is even wrong in the example I wrote for the documentation, sorry...):

```  sage: k.<a> = NumberField(x^2 + 5)
sage: N = k.ideal(3)
sage: alpha = NFCusp(k, 3, a + 1)
sage: beta = NFCusp(k, 2, a - 3)
sage: alpha.is_Gamma0_equivalent(beta, N, Transformation=True)
(True, [2*a - 4, -3*a - 4, -5*a + 2, 3*a + 13])
```

The matrix is not in Gamma0(3)!

It's not difficult to compute the right matrix. I'll be happy to write a patch in a few weeks (after I submit my thesis).

### comment:1 Changed 11 years ago by mtaranes

• Status changed from new to needs_review

Here is a patch, based on Sage 4.6.

### comment:2 follow-up: ↓ 3 Changed 11 years ago by davidloeffler

• Authors set to Maite Aranes
• Milestone set to sage-4.6.2
• Reviewers set to David Loeffler
• Status changed from needs_review to positive_review

Looks fine to me, and all doctests in sage/modular pass. (I set the milestone to 4.6.2, as 4.6.1 is in feature freeze, I believe).

### comment:3 in reply to: ↑ 2 Changed 11 years ago by cremona

Looks fine to me, and all doctests in sage/modular pass. (I set the milestone to 4.6.2, as 4.6.1 is in feature freeze, I believe).

Thanks, David -- it would quite nice to get this in before Maite's viva (Jan 27th)!

### comment:4 Changed 11 years ago by jdemeyer

• Milestone changed from sage-4.6.2 to sage-4.6.1

Milestone set back to 4.6.1 by special request from John Cremona.

### comment:5 Changed 11 years ago by jdemeyer

• Merged in set to sage-4.6.1.rc0
• Resolution set to fixed
• Status changed from positive_review to closed
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