# Subspaces of modular forms for Hecke triangle groups#

AUTHORS:

• Jonas Jermann (2013): initial version

sage.modular.modform_hecketriangle.subspace.ModularFormsSubSpace(*args, **kwargs)#

Create a modular forms subspace generated by the supplied arguments if possible. Instead of a list of generators also multiple input arguments can be used. If `reduce=True` then the corresponding ambient space is choosen as small as possible. If no subspace is available then the ambient space is returned.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.subspace import ModularFormsSubSpace
sage: from sage.modular.modform_hecketriangle.space import ModularForms
sage: MF = ModularForms()
sage: subspace = ModularFormsSubSpace(MF.E4()^3, MF.E6()^2+MF.Delta(), MF.Delta())
sage: subspace
Subspace of dimension 2 of ModularForms(n=3, k=12, ep=1) over Integer Ring
sage: subspace.ambient_space()
ModularForms(n=3, k=12, ep=1) over Integer Ring
sage: subspace.gens()
[1 + 720*q + 179280*q^2 + 16954560*q^3 + 396974160*q^4 + O(q^5), 1 - 1007*q + 220728*q^2 + 16519356*q^3 + 399516304*q^4 + O(q^5)]
sage: ModularFormsSubSpace(MF.E4()^3-MF.E6()^2, reduce=True).ambient_space()
CuspForms(n=3, k=12, ep=1) over Integer Ring
sage: ModularFormsSubSpace(MF.E4()^3-MF.E6()^2, MF.J_inv()*MF.E4()^3, reduce=True)
WeakModularForms(n=3, k=12, ep=1) over Integer Ring
```
class sage.modular.modform_hecketriangle.subspace.SubSpaceForms(ambient_space, basis, check)#

Submodule of (Hecke) forms in the given ambient space for the given basis.

basis()#

Return the basis of `self` in the ambient space.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.space import ModularForms
sage: MF = ModularForms(n=6, k=20, ep=1)
sage: subspace = MF.subspace([(MF.Delta()*MF.E4()^2).as_ring_element(), MF.gen(0)])
sage: subspace.basis()
[q + 78*q^2 + 2781*q^3 + 59812*q^4 + O(q^5), 1 + 360360*q^4 + O(q^5)]
sage: subspace.basis()[0].parent() == MF
True
```
change_ambient_space(new_ambient_space)#

Return a new subspace with the same basis but inside a different ambient space (if possible).

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.space import ModularForms, QuasiModularForms
sage: MF = ModularForms(n=6, k=20, ep=1)
sage: subspace = MF.subspace([MF.Delta()*MF.E4()^2, MF.gen(0)])
sage: new_ambient_space = QuasiModularForms(n=6, k=20, ep=1)
sage: subspace.change_ambient_space(new_ambient_space)    # long time
Subspace of dimension 2 of QuasiModularForms(n=6, k=20, ep=1) over Integer Ring
```
change_ring(new_base_ring)#

Return the same space as `self` but over a new base ring `new_base_ring`.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.space import ModularForms
sage: MF = ModularForms(n=6, k=20, ep=1)
sage: subspace = MF.subspace([MF.Delta()*MF.E4()^2, MF.gen(0)])
sage: subspace.change_ring(QQ)
Subspace of dimension 2 of ModularForms(n=6, k=20, ep=1) over Rational Field
sage: subspace.change_ring(CC)
Traceback (most recent call last):
...
NotImplementedError
```
contains_coeff_ring()#

Return whether `self` contains its coefficient ring.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.space import ModularForms
sage: MF = ModularForms(k=0, ep=1, n=8)
sage: subspace = MF.subspace([1])
sage: subspace.contains_coeff_ring()
True
sage: subspace = MF.subspace([])
sage: subspace.contains_coeff_ring()
False
sage: MF = ModularForms(k=0, ep=-1, n=8)
sage: subspace = MF.subspace([])
sage: subspace.contains_coeff_ring()
False
```
coordinate_vector(v)#

Return the coordinate vector of `v` with respect to the basis `self.gens()`.

INPUT:

• `v` – An element of `self`.

OUTPUT:

The coordinate vector of `v` with respect to the basis `self.gens()`.

Note: The coordinate vector is not an element of `self.module()`.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.space import ModularForms, QuasiCuspForms
sage: MF = ModularForms(n=6, k=20, ep=1)
sage: subspace = MF.subspace([(MF.Delta()*MF.E4()^2).as_ring_element(), MF.gen(0)])
sage: subspace.coordinate_vector(MF.gen(0) + MF.Delta()*MF.E4()^2).parent()
Vector space of dimension 2 over Fraction Field of Univariate Polynomial Ring in d over Integer Ring
sage: subspace.coordinate_vector(MF.gen(0) + MF.Delta()*MF.E4()^2)
(1, 1)

sage: MF = ModularForms(n=4, k=24, ep=-1)
sage: subspace = MF.subspace([MF.gen(0), MF.gen(2)])
sage: subspace.coordinate_vector(subspace.gen(0)).parent()
Vector space of dimension 2 over Fraction Field of Univariate Polynomial Ring in d over Integer Ring
sage: subspace.coordinate_vector(subspace.gen(0))
(1, 0)

sage: MF = QuasiCuspForms(n=infinity, k=12, ep=1)
sage: subspace = MF.subspace([MF.Delta(), MF.E4()*MF.f_inf()*MF.E2()*MF.f_i(), MF.E4()*MF.f_inf()*MF.E2()^2, MF.E4()*MF.f_inf()*(MF.E4()-MF.E2()^2)])
sage: el = MF.E4()*MF.f_inf()*(7*MF.E4() - 3*MF.E2()^2)
sage: subspace.coordinate_vector(el)
(7, 0, -3)
sage: subspace.ambient_coordinate_vector(el)
(7, 21/(8*d), 0, -3)
```
degree()#

Return the degree of `self`.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.space import ModularForms
sage: MF = ModularForms(n=6, k=20, ep=1)
sage: subspace = MF.subspace([(MF.Delta()*MF.E4()^2).as_ring_element(), MF.gen(0)])
sage: subspace.degree()
4
sage: subspace.degree() == subspace.ambient_space().degree()
True
```
dimension()#

Return the dimension of `self`.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.space import ModularForms
sage: MF = ModularForms(n=6, k=20, ep=1)
sage: subspace = MF.subspace([(MF.Delta()*MF.E4()^2).as_ring_element(), MF.gen(0)])
sage: subspace.dimension()
2
sage: subspace.dimension() == len(subspace.gens())
True
```
gens()#

Return the basis of `self`.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.space import ModularForms
sage: MF = ModularForms(n=6, k=20, ep=1)
sage: subspace = MF.subspace([(MF.Delta()*MF.E4()^2).as_ring_element(), MF.gen(0)])
sage: subspace.gens()
[q + 78*q^2 + 2781*q^3 + 59812*q^4 + O(q^5), 1 + 360360*q^4 + O(q^5)]
sage: subspace.gens()[0].parent() == subspace
True
```
rank()#

Return the rank of `self`.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.space import ModularForms
sage: MF = ModularForms(n=6, k=20, ep=1)
sage: subspace = MF.subspace([(MF.Delta()*MF.E4()^2).as_ring_element(), MF.gen(0)])
sage: subspace.rank()
2
sage: subspace.rank() == subspace.dimension()
True
```
sage.modular.modform_hecketriangle.subspace.canonical_parameters(ambient_space, basis, check=True)#

Return a canonical version of the parameters. In particular the list/tuple `basis` is replaced by a tuple of linearly independent elements in the ambient space.

If `check=False` (default: `True`) then `basis` is assumed to already be a basis.

EXAMPLES:

```sage: from sage.modular.modform_hecketriangle.subspace import canonical_parameters
sage: from sage.modular.modform_hecketriangle.space import ModularForms
sage: MF = ModularForms(n=6, k=12, ep=1)
sage: canonical_parameters(MF, [MF.Delta().as_ring_element(), MF.gen(0), 2*MF.gen(0)])
(ModularForms(n=6, k=12, ep=1) over Integer Ring,
(q + 30*q^2 + 333*q^3 + 1444*q^4 + O(q^5),
1 + 26208*q^3 + 530712*q^4 + O(q^5)))
```