# Root system data for type F¶

class sage.combinat.root_system.type_F.AmbientSpace(root_system, base_ring)

The lattice behind $$F_4$$. The computations are based on Bourbaki, Groupes et Algebres de Lie, Ch. 4,5,6 (planche VIII).

dimension()

Return the dimension of self.

EXAMPLES:

sage: e = RootSystem(['F',4]).ambient_space()
sage: e.dimension()
4

fundamental_weights()

Return the fundamental weights of self.

EXAMPLES:

sage: e =  RootSystem(['F',4]).ambient_space()
sage: e.fundamental_weights()
Finite family {1: (1, 1, 0, 0), 2: (2, 1, 1, 0), 3: (3/2, 1/2, 1/2, 1/2), 4: (1, 0, 0, 0)}

negative_roots()

Return the negative roots.

EXAMPLES:

sage: e = RootSystem(['F',4]).ambient_space()
sage: e.negative_roots()
[(-1, 0, 0, 0),
(0, -1, 0, 0),
(0, 0, -1, 0),
(0, 0, 0, -1),
(-1, -1, 0, 0),
(-1, 0, -1, 0),
(-1, 0, 0, -1),
(0, -1, -1, 0),
(0, -1, 0, -1),
(0, 0, -1, -1),
(-1, 1, 0, 0),
(-1, 0, 1, 0),
(-1, 0, 0, 1),
(0, -1, 1, 0),
(0, -1, 0, 1),
(0, 0, -1, 1),
(-1/2, -1/2, -1/2, -1/2),
(-1/2, -1/2, -1/2, 1/2),
(-1/2, -1/2, 1/2, -1/2),
(-1/2, -1/2, 1/2, 1/2),
(-1/2, 1/2, -1/2, -1/2),
(-1/2, 1/2, -1/2, 1/2),
(-1/2, 1/2, 1/2, -1/2),
(-1/2, 1/2, 1/2, 1/2)]

positive_roots()

Return the positive roots.

These are the roots which are positive with respect to the lexicographic ordering of the basis elements ($$\epsilon_1<\epsilon_2<\epsilon_3<\epsilon_4$$).

EXAMPLES:

sage: e = RootSystem(['F',4]).ambient_space()
sage: e.positive_roots()
[(1, 0, 0, 0),
(0, 1, 0, 0),
(0, 0, 1, 0),
(0, 0, 0, 1),
(1, 1, 0, 0),
(1, 0, 1, 0),
(1, 0, 0, 1),
(0, 1, 1, 0),
(0, 1, 0, 1),
(0, 0, 1, 1),
(1, -1, 0, 0),
(1, 0, -1, 0),
(1, 0, 0, -1),
(0, 1, -1, 0),
(0, 1, 0, -1),
(0, 0, 1, -1),
(1/2, 1/2, 1/2, 1/2),
(1/2, 1/2, 1/2, -1/2),
(1/2, 1/2, -1/2, 1/2),
(1/2, 1/2, -1/2, -1/2),
(1/2, -1/2, 1/2, 1/2),
(1/2, -1/2, 1/2, -1/2),
(1/2, -1/2, -1/2, 1/2),
(1/2, -1/2, -1/2, -1/2)]
sage: e.rho()
(11/2, 5/2, 3/2, 1/2)

root(i, j=None, k=None, l=None, p1=0, p2=0, p3=0, p4=0)

Compute a root from base elements of the underlying lattice. The arguments specify the basis elements and the signs. Sadly, the base elements are indexed zero-based. We assume that if one of the indices is not given, the rest are not as well.

EXAMPLES:

sage: e = RootSystem(['F',4]).ambient_space()
sage: [ e.root(i,j,p2=1) for i in xrange(e.n) for j in xrange(i+1,e.n) ]
[(1, -1, 0, 0), (1, 0, -1, 0), (1, 0, 0, -1), (0, 1, -1, 0), (0, 1, 0, -1), (0, 0, 1, -1)]

simple_root(i)

Return the $$i$$-th simple root.

It is computed according to what Bourbaki calls the Base:

$\alpha_1 = \epsilon_2-\epsilon_3, \alpha_2 = \epsilon_3-\epsilon_4, \alpha_3 = \epsilon_4, \alpha_4 = \frac{1}{2} \left( \epsilon_1-\epsilon_2-\epsilon_3-\epsilon_4 \right).$

EXAMPLES:

sage: e = RootSystem(['F',4]).ambient_space()
sage: e.simple_roots()
Finite family {1: (0, 1, -1, 0), 2: (0, 0, 1, -1), 3: (0, 0, 0, 1), 4: (1/2, -1/2, -1/2, -1/2)}

class sage.combinat.root_system.type_F.CartanType

EXAMPLES:

sage: ct = CartanType(['F',4])
sage: ct
['F', 4]
sage: ct._repr_(compact = True)
'F4'

sage: ct.is_irreducible()
True
sage: ct.is_finite()
True
sage: ct.is_crystallographic()
True
sage: ct.is_simply_laced()
False
sage: ct.dual()
['F', 4] relabelled by {1: 4, 2: 3, 3: 2, 4: 1}
sage: ct.affine()
['F', 4, 1]


TESTS:

sage: TestSuite(ct).run()

AmbientSpace

alias of AmbientSpace

ascii_art(label=<function <lambda> at 0x7fb316bbe5f0>)

Return an ascii art representation of the extended Dynkin diagram.

EXAMPLES:

sage: print CartanType(['F',4]).ascii_art(label = lambda x: x+2)
O---O=>=O---O
3   4   5   6

coxeter_number()

Return the Coxeter number associated with self.

EXAMPLES:

sage: CartanType(['F',4]).coxeter_number()
12

dual()

Return the dual Cartan type.

This uses that $$F_4$$ is self-dual up to relabelling.

EXAMPLES:

sage: F4 = CartanType(['F',4])
sage: F4.dual()
['F', 4] relabelled by {1: 4, 2: 3, 3: 2, 4: 1}

sage: F4.dynkin_diagram()
O---O=>=O---O
1   2   3   4
F4
sage: F4.dual().dynkin_diagram()
O---O=>=O---O
4   3   2   1
F4 relabelled by {1: 4, 2: 3, 3: 2, 4: 1}

dual_coxeter_number()

Return the dual Coxeter number associated with self.

EXAMPLES:

sage: CartanType(['F',4]).dual_coxeter_number()
9

dynkin_diagram()

Returns a Dynkin diagram for type F.

EXAMPLES:

sage: f = CartanType(['F',4]).dynkin_diagram()
sage: f
O---O=>=O---O
1   2   3   4
F4
sage: sorted(f.edges())
[(1, 2, 1), (2, 1, 1), (2, 3, 2), (3, 2, 1), (3, 4, 1), (4, 3, 1)]


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