Source code for sympy.liealgebras.type_f

from sympy.core.compatibility import range
from .cartan_type import Standard_Cartan
from sympy.core.backend import Matrix, Rational


[docs]class TypeF(Standard_Cartan): def __new__(cls, n): if n != 4: raise ValueError("n should be 4") return Standard_Cartan.__new__(cls, "F", 4)
[docs] def dimension(self): """Dimension of the vector space V underlying the Lie algebra Examples ======== >>> from sympy.liealgebras.cartan_type import CartanType >>> c = CartanType("F4") >>> c.dimension() 4 """
return 4
[docs] def basic_root(self, i, j): """Generate roots with 1 in ith position and -1 in jth position """ n = self.n root = [0]*n root[i] = 1 root[j] = -1
return root
[docs] def simple_root(self, i): """The ith simple root of F_4 Every lie algebra has a unique root system. Given a root system Q, there is a subset of the roots such that an element of Q is called a simple root if it cannot be written as the sum of two elements in Q. If we let D denote the set of simple roots, then it is clear that every element of Q can be written as a linear combination of elements of D with all coefficients non-negative. Examples ======== >>> from sympy.liealgebras.cartan_type import CartanType >>> c = CartanType("F4") >>> c.simple_root(3) [0, 0, 0, 1] """ if i < 3: return basic_root(i-1, i) if i == 3: root = [0]*4 root[3] = 1 return root if i == 4: root = [Rational(-1, 2)]*4
return root
[docs] def positive_roots(self): """Generate all the positive roots of A_n This is half of all of the roots of F_4; by multiplying all the positive roots by -1 we get the negative roots. Examples ======== >>> from sympy.liealgebras.cartan_type import CartanType >>> c = CartanType("A3") >>> c.positive_roots() {1: [1, -1, 0, 0], 2: [1, 0, -1, 0], 3: [1, 0, 0, -1], 4: [0, 1, -1, 0], 5: [0, 1, 0, -1], 6: [0, 0, 1, -1]} """ n = self.n posroots = {} k = 0 for i in range(0, n-1): for j in range(i+1, n): k += 1 posroots[k] = self.basic_root(i, j) k += 1 root = self.basic_root(i, j) root[j] = 1 posroots[k] = root for i in range(0, n): k += 1 root = [0]*n root[i] = 1 posroots[k] = root k += 1 root = [Rational(1, 2)]*n posroots[k] = root for i in range(1, 4): k += 1 root = [Rational(1, 2)]*n root[i] = Rational(-1, 2) posroots[k] = root posroots[k+1] = [Rational(1, 2), Rational(1, 2), Rational(-1, 2), Rational(-1, 2)] posroots[k+2] = [Rational(1, 2), Rational(-1, 2), Rational(1, 2), Rational(-1, 2)] posroots[k+3] = [Rational(1, 2), Rational(-1, 2), Rational(-1, 2), Rational(1, 2)] posroots[k+4] = [Rational(1, 2), Rational(-1, 2), Rational(-1, 2), Rational(-1, 2)]
return posroots
[docs] def roots(self): """ Returns the total number of roots for F_4 """
return 48
[docs] def cartan_matrix(self): """The Cartan matrix for F_4 The Cartan matrix matrix for a Lie algebra is generated by assigning an ordering to the simple roots, (alpha[1], ...., alpha[l]). Then the ijth entry of the Cartan matrix is (<alpha[i],alpha[j]>). Examples ======== >>> from sympy.liealgebras.cartan_type import CartanType >>> c = CartanType('A4') >>> c.cartan_matrix() Matrix([ [ 2, -1, 0, 0], [-1, 2, -1, 0], [ 0, -1, 2, -1], [ 0, 0, -1, 2]]) """ m = Matrix( 4, 4, [2, -1, 0, 0, -1, 2, -2, 0, 0, -1, 2, -1, 0, 0, -1, 2])
return m
[docs] def basis(self): """ Returns the number of independent generators of F_4 """
return 52 def dynkin_diagram(self): diag = "0---0=>=0---0\n" diag += " ".join(str(i) for i in range(1, 5))
return diag