7.5.2 modular.modsym.modsym - Create modular symbols spaces

The module modular.modsym.modsym defines the following methods:

ModularSymbols( [group=Rational Field], [weight=0], [sign=2], [base_field=1])

Create an ambient space of modular symbols.

INPUT:
    group -- The congruence subgroup or a Dirichlet
             character eps

weight - int, the weight, which must be >= 2.

sign - int, The sign of the involution on modular symbols induced by complex conjugation. The default is 0, which means"no sign", i.e., take the whole space.

base_field - field (default is the field of rational numbers). The base field is ignored if group is a character.

First we create some spaces with trivial character:

sage: ModularSymbols(Gamma0(11),2).dimension()
3
sage: ModularSymbols(Gamma0(1),12).dimension()
3

If we give an integer N for the congruence subgroup, it defaults to $ \Gamma_0(N)$ :

sage: ModularSymbols(1,12,-1).dimension()
1
sage: ModularSymbols(11,4, sign=1)
Full Modular Symbols space for Gamma_0(11) of weight 4 and
dimension 4 over Rational Field

We create some spaces for $ \Gamma_1(N)$ .

sage: ModularSymbols(Gamma1(13),2)
Full Modular Symbols space for Gamma_1(13) of weight 2 and
dimension 15 over Rational Field
sage: ModularSymbols(Gamma1(13),2, sign=1).dimension()
13
sage: ModularSymbols(Gamma1(13),2, sign=-1).dimension()
2
sage: [ModularSymbols(Gamma1(7),k).dimension() for k in [2,3,4,5]]
[5, 8, 12, 16]
sage: ModularSymbols(Gamma1(5),11).dimension()
20

We create a space with character:

sage: e = DirichletGroup(13).gen()**2
sage: e.order()
6
sage: M = ModularSymbols(e, 2); M
Full Modular Symbols space of level 13, weight 2, character
[zeta_12^2] and dimension 4 over Cyclotomic Field of order 12
and degree 4
sage: f = M.T(2).charpoly(); f
x^4 + (-zeta_12^2 - 1)*x^3 + (-8*zeta_12^2)*x^2 + (10*zeta_12^2
- 5)*x + 21*zeta_12^2 - 21
sage: f.factor()
[(x + -2*zeta_12^2 - 1, 1), (x + -zeta_12^2 - 2, 1), (x +
zeta_12^2 + 1, 2)]

More examples of spaces with character:

sage: e = DirichletGroup(5, RationalField()).gen(); e
[-1]
sage: m = ModularSymbols(e, 2); m
Full Modular Symbols space of level 5, weight 2, character [-1]
and dimension 2 over Rational Field

sage: m.T(2).charpoly()
x^2 - 1
sage: m = ModularSymbols(e, 6); m.dimension()
6
sage: m.T(2).charpoly()
x^6 - 873*x^4 - 82632*x^2 - 1860496

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