def order_at_cusp(self, cusp: 'CuspFamily') -> Integer:
r"""
Return the order of vanishing of ``self`` at the given cusp.
INPUT:
- ``cusp`` -- a :class:`CuspFamily` object
OUTPUT:
- an integer
EXAMPLES::
sage: e = EtaProduct(2, {2:24, 1:-24})
sage: e.order_at_cusp(CuspFamily(2, 1)) # cusp at infinity
1
sage: e.order_at_cusp(CuspFamily(2, 2)) # cusp 0
-1
"""
if not isinstance(cusp, CuspFamily):
raise TypeError("argument (=%s) should be a CuspFamily" % cusp)
if cusp.level() != self._N:
raise ValueError("cusp not on right curve")
sigma = sum(ell * self._rdict[ell] / cusp.width() *
(gcd(cusp.width(), self._N // ell))**2
for ell in self._rdict)
return sigma / ZZ(24) / gcd(cusp.width(), self._N // cusp.width())
def kernel_vector(self, way='LLL', verbose=False):
r"""
todo: clean this
EXAMPLES::
sage: from slabbe import ChristoffelGraph
sage: C = ChristoffelGraph((2,5,7))
sage: C.kernel_vector()
[(-1, -1, 1), (3, -4, 0)]
"""
from sage.arith.misc import gcd
if way == 'vect_gcd':
a,b,c = self._v
gcd_ac = gcd(a,c)
gcd_bc = gcd(b,c)
U = ua,ub,uc = vector((c,0,-a)) / gcd(a,c)
V = va,vb,vc = vector((0,c,-b)) / gcd(b,c)
rows = U,V
elif way == 'echelon':
a,b,c = self._v
m = matrix(ZZ, 4, [1,1,1,c,0,-a,0,c,-b,b,-a,0])
me = m.echelon_form()
if verbose:
print(me)
rows = me[1],me[2]
elif way == 'LLL':
dim = self.dimension()
if dim == 3:
a,b,c = self._v
M = matrix(ZZ, 4, [1,1,1,c,0,-a,0,c,-b,b,-a,0])
elif dim == 4:
a,b,c,d = self._v
M = matrix(ZZ, 7, (1,1,1,1,b,-a,0,0,c,0,-a,0,0,c,-b,0,d,0,0,-a,0,d,0,-b,0,0,d,-c))
else:
raise ValueError("dimension (=%s) must be 3 or 4" % dim)
rows = M.LLL().rows()
VS = rows[0].parent()
zero = VS(0)
un = VS((1,)*dim)
assert zero in rows, "(0,0,0) not in LLL result"
assert un in rows, "(1,1,1) not in LLL result"
while zero in rows: rows.remove(zero)
while un in rows: rows.remove(un)
elif way == 'vect':
a,b,c = self._v
U = ua,ub,uc = vector((c,0,-a))
V = va,vb,vc = vector((0,c,-b))
rows = U,V
else:
raise ValueError("unknown way")
R = matrix(rows)
if sum(map(abs, R.minors(dim-1))) != sum(map(abs,self._v)):
print(R)
print(R.minors(dim-1))
print(sum(map(abs, R.minors(dim))))
print(sum(map(abs,self._v)))
raise Exception("The result (=%s) is false " % rows)
return rows
def __init__(self,
V,
W,
gens=None,
modulus=None,
modulus_qf=None,
check=True):
r"""
Initialize ``self``.
TESTS::
sage: from sage.modules.torsion_quadratic_module import TorsionQuadraticModule
sage: T = TorsionQuadraticModule(ZZ^3, 6*ZZ^3)
sage: TestSuite(T).run()
"""
if check:
if V.rank() != W.rank():
raise ValueError("modules must be of the same rank")
if V.base_ring() is not ZZ:
raise NotImplementedError("only currently implemented over ZZ")
if V.inner_product_matrix() != V.inner_product_matrix().transpose(
):
raise ValueError(
"the cover must have a symmetric inner product")
if gens is not None and V.span(gens) + W != V:
raise ValueError("provided gens do not generate the quotient")
FGP_Module_class.__init__(self, V, W, check=check)
if gens is not None:
self._gens_user = tuple(self(v) for v in gens)
else:
# this is taken care of in the .gens method
# we do not want this at initialization
self._gens_user = None
# compute the modulus - this may be expensive
if modulus is None or check:
# The inner product of two elements `b(v1+W,v2+W)`
# is defined `mod (V,W)`
num = V.basis_matrix() * V.inner_product_matrix() * W.basis_matrix(
).T
self._modulus = gcd(num.list())
if modulus is not None:
if check and self._modulus / modulus not in self.base_ring():
raise ValueError("the modulus must divide (V, W)")
self._modulus = modulus
if modulus_qf is None or check:
# The quadratic_product of an element `q(v+W)` is defined
# `\mod 2(V,W) + ZZ\{ (w,w) | w in w\}`
norm = gcd(self.W().gram_matrix().diagonal())
self._modulus_qf = gcd(norm, 2 * self._modulus)
if modulus_qf is not None:
if check and self._modulus_qf / modulus_qf not in self.base_ring():
raise ValueError("the modulus_qf must divide (V, W)")
self._modulus_qf = modulus_qf
def is_irreducible_2cyl(w1,h1,t1,w2,h2,t2):
r"""
Test of irreducibility.
"""
print "testing", w1, h1, t1, w2, h2, t2
print " result heights gcd(%d,%d) = %d" %(h1,h2,gcd(h1,h2)), "and", gcd([w1, w2, h2*t1-h1*t2]) == 1
return gcd(h1,h2) == 1 and gcd([w1, w2, h2*t1-h1*t2]) == 1
def __classcall__(cls,
V,
W,
gens=None,
modulus=None,
modulus_qf=None,
check=True):
r"""
Return a :class:`TorsionQuadraticModule`.
This method does the preprocessing for :meth:`sage.structure.CachedRepresentation`.
TESTS::
sage: q = matrix([1/2])
sage: D1 = TorsionQuadraticForm(q)
sage: D2 = TorsionQuadraticForm(q)
sage: D1 is D2
True
"""
if check:
if V.rank() != W.rank():
raise ValueError("modules must be of the same rank")
if V.base_ring() is not ZZ:
raise NotImplementedError("only currently implemented over ZZ")
if V.inner_product_matrix() != V.inner_product_matrix().transpose(
):
raise ValueError(
"the cover must have a symmetric inner product")
if gens is not None and V.span(gens) + W != V:
raise ValueError("provided gens do not generate the quotient")
# compute the modulus - this may be expensive
if modulus is None or check:
# The inner product of two elements `b(v1+W,v2+W)`
# is defined `mod (V,W)`
num = V.basis_matrix() * V.inner_product_matrix() * W.basis_matrix(
).T
max_modulus = gcd(num.list())
if modulus is None:
modulus = max_modulus
elif check and max_modulus / modulus not in V.base_ring():
raise ValueError("the modulus must divide (V, W)")
if modulus_qf is None or check:
# The quadratic_product of an element `q(v+W)` is defined
# `\mod 2(V,W) + ZZ\{ (w,w) | w in w\}`
norm = gcd(W.gram_matrix().diagonal())
max_modulus_qf = gcd(norm, 2 * modulus)
if modulus_qf is None:
modulus_qf = max_modulus_qf
elif check and max_modulus_qf / modulus_qf not in V.base_ring():
raise ValueError("the modulus_qf must divide (V, W)")
return super(TorsionQuadraticModule,
cls).__classcall__(cls, V, W, gens, modulus, modulus_qf)
def shift_cusp(gamma, t):
r"""
Returns gamma_2, delta such that B_t * gamma = gamma_2 * delta
INPUT:
- gamma - SL_2(Z) matrix
- t - int, corresponds to the level shift B_t
OUTPUT:
- gamma, delta - gamma in SL_2(Z), delta triangular with B_t * gamma = gamma_2 * delta
"""
a, c = gamma[0][0], gamma[1][0]
gamma_2 = complete_column(a * t / gcd(a * t, c), c / gcd(a * t, c))
delta = gamma_2**(-1) * Matrix([[t, 0], [0, 1]]) * gamma
return gamma_2, delta
def is_primitive(self, M):
r"""
Return whether ``M`` is a primitive submodule of this lattice.
A `\ZZ`-submodule ``M`` of a `\ZZ`-module ``L`` is called primitive if
the quotient ``L/M`` is torsion free.
INPUT:
- ``M`` -- a submodule of this lattice
EXAMPLES::
sage: U = IntegralLattice("U")
sage: L1 = U.span([vector([1,1])])
sage: L2 = U.span([vector([1,-1])])
sage: U.is_primitive(L1)
True
sage: U.is_primitive(L2)
True
sage: U.is_primitive(L1+L2)
False
We can also compute the index::
sage: (L1+L2).index_in(U)
2
"""
return (gcd((self / M).invariants()) == 0)
def is_primitive(self, M):
r"""
Return whether ``M`` is a primitive submodule of this lattice.
A `\ZZ`-submodule ``M`` of a `\ZZ`-module ``L`` is called primitive if
the quotient ``L/M`` is torsion free.
INPUT:
- ``M`` -- a submodule of this lattice
EXAMPLES::
sage: U = IntegralLattice("U")
sage: L1 = U.span([vector([1,1])])
sage: L2 = U.span([vector([1,-1])])
sage: U.is_primitive(L1)
True
sage: U.is_primitive(L2)
True
sage: U.is_primitive(L1+L2)
False
We can also compute the index::
sage: (L1+L2).index_in(U)
2
"""
return (gcd((self/M).invariants()) == 0)
def is_primitive(self, M):
r"""
Return whether ``M`` is a primitive submodule of this lattice.
A `\Z`-submodule ``M`` of a `\Z`-module ``L`` is called primitive if
the quotient ``L/M`` is torsion free.
INPUT:
- ``M`` -- a submodule of this lattice
EXAMPLES::
sage: from sage.modules.free_quadratic_module_integer_symmetric import IntegralLattice
sage: U = IntegralLattice(Matrix(ZZ,2,2,[0,1,1,0]))
sage: L1 = U.span([vector([1,1])])
sage: L2 = U.span([vector([1,-1])])
sage: U.is_primitive(L1)
True
sage: U.is_primitive(L2)
True
sage: U.is_primitive(L1+L2)
False
We can also compute the index::
sage: (L1+L2).index_in(U)
2
"""
return (gcd((self/M).invariants()) == 0)
def trace_of_frobenius_mod_2(E):
F = E.base_field()
x = PolynomialRing(F, 'x').gen()
f = x ** 3 + E.a4() * x + E.a6()
q = F.order()
if gcd(f, power_mod(x, q, f) - x).is_constant():
return 1
else:
return 0
def taut_polynomial(tri, angle, cycles = [], alpha = True, mode = "taut"):
# set up
ZH = group_ring(tri, angle, cycles, alpha = alpha)
P = ZH.polynomial_ring()
ET = edges_to_triangles_matrix(tri, angle, cycles, ZH, P, mode = mode)
# compute via minors
minors = ET.minors(tri.countTetrahedra())
return normalise_poly(gcd(minors), ZH, P)
def complete_row(a, c, i=1):
"""
Completes a row a,c with gcd(a,c) = 1 to an SL_2(Z)-matrix.
INPUT:
- a - int, the top entry of the column.
- c - int, the bottom entry of the column.
- i - int.
OUTPUT:
- A matrix in SL_2(Z) with i-th column [a,c]
"""
if gcd(a, c) > 1:
raise ValueError('Input needs to be coprime')
return complete_column(a, c, i).T
def origami_H2_2cyl_iterator(n, reducible=False, output="coordinates"):
r"""
INPUT:
- ``n`` - positive integer - the number of squares
- ``reducible`` - bool (default: False) - if True returns also the reducible
origamis.
- ``output`` - either "coordinates" or "origami" or "standard origami"
"""
for n1,n2 in OrderedPartitions(n,k=2):
for w1 in divisors(n1):
h1 = n1//w1
for w2 in filter(lambda x: x < w1, divisors(n2)):
h2 = n2//w2
if reducible or gcd(h1,h2) == 1:
d = gcd(w1,w2)
if d == 1:
for t1 in xrange(w1):
for t2 in xrange(w2):
if output == "coordinates":
yield w1,h1,t1,w2,h2,t2
elif output == "origami":
yield origami_H2_2cyl(w1,h1,t1,w2,h2,t2)
elif output == "standard_origami":
yield origami_H2_2cyl(w1,h1,t1,w2,h2,t2).standard_form()
else:
for t1 in xrange(w1):
for t2 in xrange(w2):
if reducible or gcd(d,h2*t1-h1*t2) == 1:
if output == "coordinates":
yield w1,h1,t1,w2,h2,t2
elif output == "origami":
yield origami_H2_2cyl(w1,h1,t1,w2,h2,t2)
elif output == "standard_origami":
yield origami_H2_2cyl(w1,h1,t1,w2,h2,t2).standard_form()
def __init__(self, V, W, gens=None, modulus=None, modulus_qf=None, check=True):
r"""
Initialize ``self``.
TESTS::
sage: from sage.modules.torsion_quadratic_module import TorsionQuadraticModule
sage: T = TorsionQuadraticModule(ZZ^3, 6*ZZ^3)
sage: TestSuite(T).run()
"""
if check:
if V.rank() != W.rank():
raise ValueError("modules must be of the same rank")
if V.base_ring() is not ZZ:
raise NotImplementedError("only currently implemented over ZZ")
if V.inner_product_matrix() != V.inner_product_matrix().transpose():
raise ValueError("the cover must have a symmetric inner product")
if gens is not None and V.span(gens) + W != V:
raise ValueError("provided gens do not generate the quotient")
FGP_Module_class.__init__(self, V, W, check=check)
if gens is None:
self._gens = FGP_Module_class.gens(self)
else:
self._gens = [self(v) for v in gens]
if modulus is not None:
if check:
# The inner product of two elements `b(v1+W,v2+W)` is defined `mod (V,W)`
num = gcd([x.inner_product(y) for x in V.gens()
for y in W.gens()])
if num / modulus not in self.base_ring():
raise ValueError("the modulus must divide (V, W)")
self._modulus = modulus
else:
# The inner product of two elements `b(v1+W,v2+W)` is defined `mod (V,W)`
self._modulus = gcd([x.inner_product(y) for x in V.gens()
for y in W.gens()])
if modulus_qf is not None:
if check:
# The quadratic_product of an element `q(v+W)` is defined
# `\mod 2(V,W) + ZZ\{ (w,w) | w in w\}`
norm = gcd(self.W().gram_matrix().diagonal())
num = gcd(norm, 2 * self._modulus)
if num / modulus_qf not in self.base_ring():
raise ValueError("the modulus_qf must divide (V, W)")
self._modulus_qf = modulus_qf
else:
# The quadratic_product of an element `q(v+W)` is defined
# `\mod 2(V,W) + ZZ\{ (w,w) | w in w\}`
norm = gcd(self.W().gram_matrix().diagonal())
self._modulus_qf = gcd(norm, 2 * self._modulus)
def __init__(self,
base,
names,
degrees,
max_degree,
category=None,
**kwargs):
r"""
Construct a commutative graded algebra with finite degree.
TESTS::
sage: A.<x,y,z,t> = GradedCommutativeAlgebra(QQ, max_degree=6)
sage: TestSuite(A).run()
sage: A = GradedCommutativeAlgebra(QQ, ('x','y','z'), [2,3,4], max_degree=8)
sage: TestSuite(A).run()
sage: A = GradedCommutativeAlgebra(QQ, ('x','y','z','t'), [1,2,3,4], max_degree=10)
sage: TestSuite(A).run()
"""
from sage.arith.misc import gcd
if max_degree not in ZZ:
raise TypeError('max_degree must be an integer')
if max_degree < max(degrees):
raise ValueError(f'max_degree must not deceed {max(degrees)}')
self._names = names
self.__ngens = len(self._names)
self._degrees = degrees
self._max_deg = max_degree
self._weighted_vectors = WeightedIntegerVectors(degrees)
self._mul_symbol = kwargs.pop('mul_symbol', '*')
self._mul_latex_symbol = kwargs.pop('mul_latex_symbol', '')
step = gcd(degrees)
universe = DisjointUnionEnumeratedSets(
self._weighted_vectors.subset(k)
for k in range(0, max_degree, step))
base_cat = Algebras(
base).WithBasis().Super().Supercommutative().FiniteDimensional()
category = base_cat.or_subcategory(category, join=True)
indices = ConditionSet(universe, self._valid_index)
sorting_key = self._weighted_vectors.grading
CombinatorialFreeModule.__init__(self,
base,
indices,
sorting_key=sorting_key,
category=category)
def complete_column(a, c, i=1):
"""
Completes a column a,c with gcd(a,c) = 1 to an SL_2(Z)-matrix.
INPUT:
- a - int, the top entry of the column.
- c - int, the bottom entry of the column.
- i - int.
OUTPUT:
- A matrix in SL_2(Z) with i-th column [a,c]
"""
if gcd(a, c) > 1:
raise ValueError('Input needs to be coprime')
_, d, b = xgcd(a, c)
b = -b
if i == 1:
return Matrix([[a, b], [c, d]])
elif i == 2:
return Matrix([[-b, a], [-d, c]])
def primitive_index(self):
"""
Return the primitive index.
.. SEEALSO::
:meth:`is_primitive`, :meth:`primitive_data`
EXAMPLES::
sage: from sage.modular.hypergeometric_motive import HypergeometricData as Hyp
sage: Hyp(cyclotomic=([3],[4])).primitive_index()
1
sage: Hyp(gamma_list=[-2, 4, 6, -8]).primitive_index()
2
sage: Hyp(gamma_list=[-3, 6, 9, -12]).primitive_index()
3
"""
return gcd(self.gamma_list())
def primitive_data(self):
"""
Return a primitive version.
.. SEEALSO::
:meth:`is_primitive`, :meth:`primitive_index`,
EXAMPLES::
sage: from sage.modular.hypergeometric_motive import HypergeometricData as Hyp
sage: H = Hyp(cyclotomic=([3],[4]))
sage: H2 = Hyp(gamma_list=[-2, 4, 6, -8])
sage: H2.primitive_data() == H
True
"""
g = self.gamma_list()
d = gcd(g)
return HypergeometricData(gamma_list=[x / d for x in g])
def primitive_index(self):
"""
Return the primitive index.
.. SEEALSO::
:meth:`is_primitive`, :meth:`primitive_data`
EXAMPLES::
sage: from sage.modular.hypergeometric_motive import HypergeometricData as Hyp
sage: Hyp(cyclotomic=([3],[4])).primitive_index()
1
sage: Hyp(gamma_list=[-2, 4, 6, -8]).primitive_index()
2
sage: Hyp(gamma_list=[-3, 6, 9, -12]).primitive_index()
3
"""
return gcd(self.gamma_list())
def primitive_data(self):
"""
Return a primitive version.
.. SEEALSO::
:meth:`is_primitive`, :meth:`primitive_index`
EXAMPLES::
sage: from sage.modular.hypergeometric_motive import HypergeometricData as Hyp
sage: H = Hyp(cyclotomic=([3],[4]))
sage: H2 = Hyp(gamma_list=[-2, 4, 6, -8])
sage: H2.primitive_data() == H
True
"""
g = self.gamma_list()
d = gcd(g)
return HypergeometricData(gamma_list=[x / d for x in g])
def _reduce_invariants(invariants, weights):
"""
Reduce a list of invariants of given weights.
Reduces the given invariants over a field whose rings of integers is a gcd
domain, in such a way that their greatest common weighted divisor is a unit
in this ring.
INPUT:
- ``invariants`` -- The values of the invariants.
- ``weights`` -- The respective weights of the invariants.
OUTPUT:
A list of invariants that is equivalent to the input and
has no common weighted divisor.
EXAMPLES::
sage: from sage.rings.invariants.reconstruction import _reduce_invariants
sage: invariants = [6/5, 12, 16]
sage: weights = [1, 2, 3]
sage: _reduce_invariants(invariants, weights)
[3, 75, 250]
"""
from sage.rings.integer_ring import ZZ
factors = [dict(I.factor()) for I in invariants]
scalar = ZZ(1)
n = len(weights)
from sage.arith.misc import gcd
for prime in gcd(invariants).factor():
p = prime[0]
for D in factors:
if p not in D:
D[p] = 0
scalar = scalar * p**min(
[factors[i][p] // weights[i] for i in range(n)])
return [invariants[i] * scalar**-weights[i] for i in range(n)]
def taut_polynomial_via_tree(tri, angle, cycles = [], alpha = True, mode = "taut"):
"""
If cycles = [] then this is the taut polynomial. If cycles != []
then this is the zero-Fitting invariant of the module obtained by
'extension of scalars' - that is, form the epimorphism obtained by
killing the given boundary cycles, apply it to the presentation
matrix, and only then compute the gcd of the (correct minors).
"""
# set up
ZH = group_ring(tri, angle, cycles, alpha = alpha)
P = ZH.polynomial_ring()
ET = edges_to_triangles_matrix(tri, angle, cycles, ZH, P, mode = mode)
_, non_tree_faces, _ = spanning_dual_tree(tri)
ET = ET.transpose()
ET = Matrix([row for i, row in enumerate(ET) if i in non_tree_faces]).transpose()
# compute via minors
minors = ET.minors(tri.countTetrahedra())
return normalise_poly(gcd(minors), ZH, P)
def AL(N, S):
r"""
INPUT:
- N - a positive integer
- S - a maximal divisor of N or a set of primes
OUPUT:
- A matrix representing the partial Atkin-Lehner operator W_S
"""
try:
S = prod([p**(N.valuation(p)) for p in S])
except TypeError:
if gcd(S, N / S) > 1:
S = S.prime_divisors()
S = prod([p**(N.valuation(p)) for p in S])
_, w, z = xgcd(S, N / S)
z = -z
return Matrix([[S, 1], [N * z, S * w]])
def origami_H2_1cyl_iterator(n, reducible=False, output='coordinates'):
r"""
INPUT:
- ``n`` - positive integer - the number of squares
- ``reducible`` - bool (default: False) - if True returns also the reducible
origamis.
- ``output`` - either "coordinates" or "origami" or "standard origami"
"""
if reducible:
hlist = divisors(n)
else:
hlist = [1]
for h in hlist:
for p in Partitions(Integer(n/h),length=3):
for l in CyclicPermutationsOfPartition([p]):
l1,l2,l3 = l[0]
if l1 == l2 and l2 == l3:
if reducible or l1 == 1:
for t in xrange(l1):
if output == "coordinates":
yield l1,l2,l3,h,t
elif output == "origami":
yield origami_H2_1cyl(l1,l2,l3,h,t)
elif output == "standard_origami":
yield origami_H2_1cyl(l1,l2,l3,h,t).standard_form()
elif reducible or gcd([l1,l2,l3]) == 1:
for t in xrange(n):
if output == "coordinates":
yield l1,l2,l3,h,t
elif output == "origami":
yield origami_H2_1cyl(l1,l2,l3,h,t)
elif output == "standard_origami":
yield origami_H2_1cyl(l1,l2,l3,h,t).standard_form()
def is_irreducible_1cyl(l1,l2,l3,h,t):
r"""
Test of irreducibility.
"""
return h == 1 and gcd([l1,l2,l3]) == 1
def order_of_euler_class(delta, E):
"""
Given the coboundary operator delta and an Euler two-cocycle E,
returns k if [E] is k--torsion. By convention, returns zero if
[E] is non-torsion. Note that the trivial element is 1--torsion.
"""
delta = Matrix(delta)
E = vector(E)
# Note that E is a coboundary if there is a one-cocycle C solving
#
# E = C*delta
#
# We can find C (if it exists at all) using Smith normal form.
D, U, V = delta.smith_form()
assert D == U*delta*V
# So we are trying to solve
#
# C*delta = C*U.inverse()*D*V.inverse() = E
#
# for a one-cochain C. Multiply by V to get
#
# C*delta*V = C*U.inverse()*D = E*V
#
# Now set
#
# B = C*U.inverse(), and so B*U = C
#
# and rewrite to get
#
# B*U*delta*V = B*D = E*V
#
# So define E' by:
Ep = E*V
# Finally we attempt to solve B * D = Ep. Note that D is
# diagonal: so if we can solve all of the equations
# B[i] * D[i][i] == Ep[i]
# with B[i] integers, then [E] = 0 in cohomology.
diag = diagonal(D)
if any( (diag[i] == 0 and Ep[i] != 0) for i in range(len(Ep)) ):
return 0
# All zeros are at the end in Smith normal form. Since we've
# passed the above we can now remove them.
first_zero = diag.index(0)
diag = diag[:first_zero]
Ep = Ep[:first_zero]
# Since diag[i] is (now) never zero we can divide to get the
# fractions Ep[i]/diag[i] and then find the scaling that makes
# them simultaneously integral.
denoms = [ diag[i] / gcd(Ep[i], diag[i]) for i in range(len(Ep)) ]
return lcm(denoms)
def extract_a_solution(L, m, s, A, homogeneous=False, sol_type="any"):
r"""
Return a single solution from the kernel of the matrix A.
INPUT:
- ``L`` -- a free Lie algebra quotient
- ``m`` -- the lowest degree of covectors in the matrix
- ``s`` -- the highest degree of covectors in the matrix
- ``A`` -- a matrix of the form given by :func:`abnormal_factor_system`
- ``homogeneous`` -- a boolean; whether the solved polynomial is homogeneous
- ``sol_type`` -- one of "any", "all", "nice"
With sol_type="any", the output is the solution from the first nonpivot
column of the echelon form of A.
With sol_type="all", the output is the basis of the kernel given by
the nonpivot columns of the echelon form of A.
With sol_type="nice", the output is a linear combination that attempts
to decrease the number of nonzero coefficients and their magnitudes.
OUTPUT:
A dictionary {X: c} describing a covector. Each `X` is an element of the
Lie algebra `L` and each `c` is the coefficient of the covector
for the dual element of `X`.
"""
# extract names of the covector variables
if homogeneous:
vecs = list(L.graded_basis(s))
else:
vecs = [X for k in range(m, s + 1) for X in L.graded_basis(k)]
# check that the dimensions are correct
assert A.subdivisions()[1][0] == len(vecs)
covecdim = len(vecs)
# compute the echelon form of A
EA = A.echelon_form()
def covec_to_dict(v):
covec = {}
for k, vk in enumerate(v):
if vk:
covec[vecs[k]] = vk
return covec
nonpivot = covecdim
covecs = []
while True:
# find next non-pivot column
while nonpivot in A.pivots():
nonpivot += 1
if nonpivot >= A.dimensions()[1]:
if sol_type != "any":
break
# no solution found, something is wrong
raise ValueError(
"something went wrong: no nonpivot column in the multiplier variables"
)
if sol_type == "any":
verbose("computing a solution")
else:
verbose("computing solution #%d" % (len(covecs) + 1))
# the non-pivot columns of the echelon form define the valid solutions
# rescale the column so that the covector has simplified coefficients
cv = EA.column(nonpivot)[:covecdim]
cv = cv / gcd(cv)
if sol_type == "any":
return covec_to_dict(cv)
covecs.append(cv)
nonpivot += 1
if sol_type == "all":
return [covec_to_dict(v) for v in covecs]
if A.base_ring() == QQ:
# over rationals, start with the covector with smallest coefficients
covecs = sorted(covecs, key=lambda v: min(abs(vk) for vk in v))
covec = covecs[0]
covecs = covecs[1:]
while covecs:
other = covecs[0]
covecs = covecs[1:]
# eliminate the coefficient with the largest gcd
gcdvec = [gcd(a, b) for a, b in zip(covec, other)]
i = gcdvec.index(max(gcdvec))
covec = covec[i] * other - other[i] * covec
covec = covec / gcd(covec)
# make leading coefficient positive
i = 0
while not covec[i]:
i += 1
if covec[i] < 0:
covec = -covec
return covec_to_dict(covec)
def test_norm_gcd():
for K, q, p, result in test_cases_true + test_cases_false:
qq = (q * K).factor()[0][0]
is_coprime = gcd(qq.absolute_norm(), p) == 1
assert is_coprime == result
def binary_quintic_coefficients_from_invariants(invariants, K=None, invariant_choice='default', scaling='none'):
r"""
Reconstruct a binary quintic from the values of its (Clebsch) invariants.
INPUT:
- ``invariants`` -- A list or tuple of values of the three or four
invariants. The default option requires the Clebsch invariants `A`, `B`,
`C` and `R` of the binary quintic.
- ``K`` -- The field over which the quintic is defined.
- ``invariant_choice`` -- The type of invariants provided. The accepted
options are ``'clebsch'`` and ``'default'``, which are the same. No
other options are implemented.
- ``scaling`` -- How the coefficients should be scaled. The accepted
values are ``'none'`` for no scaling, ``'normalized'`` to scale in such
a way that the resulting coefficients are independent of the scaling of
the input invariants and ``'coprime'`` which scales the input invariants
by dividing them by their gcd.
OUTPUT:
A set of coefficients of a binary quintic, whose invariants are equal to
the given ``invariants`` up to a scaling.
EXAMPLES:
First we check the general case, where the invariant `M` is non-zero::
sage: R.<x0, x1> = QQ[]
sage: p = 3*x1^5 + 6*x1^4*x0 + 3*x1^3*x0^2 + 4*x1^2*x0^3 - 5*x1*x0^4 + 4*x0^5
sage: quintic = invariant_theory.binary_quintic(p, x0, x1)
sage: invs = quintic.clebsch_invariants(as_tuple=True)
sage: reconstructed = invariant_theory.binary_form_from_invariants(5, invs, variables=quintic.variables()) # indirect doctest
sage: reconstructed
Binary quintic with coefficients (9592267437341790539005557/244140625000000,
2149296928207625556323004064707/610351562500000000,
11149651890347700974453304786783/76293945312500000,
122650775751894638395648891202734239/47683715820312500000,
323996630945706528474286334593218447/11920928955078125000,
1504506503644608395841632538558481466127/14901161193847656250000)
We can see that the invariants of the reconstructed form match the ones of
the original form by scaling the invariants `B` and `C`::
sage: scale = invs[0]/reconstructed.A_invariant()
sage: invs[1] == reconstructed.B_invariant()*scale^2
True
sage: invs[2] == reconstructed.C_invariant()*scale^3
True
If we compare the form obtained by this reconstruction to the one found by
letting the covariants `\alpha` and `\beta` be the coordinates of the form,
we find the forms are the same up to a power of the determinant of `\alpha`
and `\beta`::
sage: alpha = quintic.alpha_covariant()
sage: beta = quintic.beta_covariant()
sage: g = matrix([[alpha(x0=1,x1=0),alpha(x0=0,x1=1)],[beta(x0=1,x1=0),beta(x0=0,x1=1)]])^-1
sage: transformed = tuple([g.determinant()^-5*x for x in quintic.transformed(g).coeffs()])
sage: transformed == reconstructed.coeffs()
True
This can also be seen by computing the `\alpha` covariant of the obtained
form::
sage: reconstructed.alpha_covariant().coefficient(x1)
0
sage: reconstructed.alpha_covariant().coefficient(x0) != 0
True
If the invariant `M` vanishes, then the coefficients are computed in a
different way::
sage: [A,B,C] = [3,1,2]
sage: M = 2*A*B - 3*C
sage: M
0
sage: from sage.rings.invariants.reconstruction import binary_quintic_coefficients_from_invariants
sage: reconstructed = binary_quintic_coefficients_from_invariants([A,B,C])
sage: reconstructed
(-66741943359375/2097152,
-125141143798828125/134217728,
0,
52793920040130615234375/34359738368,
19797720015048980712890625/1099511627776,
-4454487003386020660400390625/17592186044416)
sage: newform = sum([ reconstructed[i]*x0^i*x1^(5-i) for i in range(6) ])
sage: newquintic = invariant_theory.binary_quintic(newform, x0, x1)
sage: scale = 3/newquintic.A_invariant()
sage: [3, newquintic.B_invariant()*scale^2, newquintic.C_invariant()*scale^3]
[3, 1, 2]
Several special cases::
sage: quintic = invariant_theory.binary_quintic(x0^5 - x1^5, x0, x1)
sage: invs = quintic.clebsch_invariants(as_tuple=True)
sage: binary_quintic_coefficients_from_invariants(invs)
(1, 0, 0, 0, 0, 1)
sage: quintic = invariant_theory.binary_quintic(x0*x1*(x0^3-x1^3), x0, x1)
sage: invs = quintic.clebsch_invariants(as_tuple=True)
sage: binary_quintic_coefficients_from_invariants(invs)
(0, 1, 0, 0, 1, 0)
sage: quintic = invariant_theory.binary_quintic(x0^5 + 10*x0^3*x1^2 - 15*x0*x1^4, x0, x1)
sage: invs = quintic.clebsch_invariants(as_tuple=True)
sage: binary_quintic_coefficients_from_invariants(invs)
(1, 0, 10, 0, -15, 0)
sage: quintic = invariant_theory.binary_quintic(x0^2*(x0^3 + x1^3), x0, x1)
sage: invs = quintic.clebsch_invariants(as_tuple=True)
sage: binary_quintic_coefficients_from_invariants(invs)
(1, 0, 0, 1, 0, 0)
sage: quintic = invariant_theory.binary_quintic(x0*(x0^4 + x1^4), x0, x1)
sage: invs = quintic.clebsch_invariants(as_tuple=True)
sage: binary_quintic_coefficients_from_invariants(invs)
(1, 0, 0, 0, 1, 0)
For fields of characteristic 2, 3 or 5, there is no reconstruction
implemented. This is part of :trac:`26786`.::
sage: binary_quintic_coefficients_from_invariants([3,1,2], K=GF(5))
Traceback (most recent call last):
...
NotImplementedError: no reconstruction of binary quintics implemented for fields of characteristic 2, 3 or 5
TESTS::
sage: from sage.rings.invariants.reconstruction import binary_quintic_coefficients_from_invariants
sage: binary_quintic_coefficients_from_invariants([1,2,3], scaling='unknown')
Traceback (most recent call last):
...
ValueError: unknown scaling option 'unknown'
"""
if invariant_choice not in ['default', 'clebsch']:
raise ValueError('unknown choice of invariants {} for a binary quintic'
.format(invariant_choice))
if scaling not in ['none', 'normalized', 'coprime']:
raise ValueError("unknown scaling option '%s'" % scaling)
if scaling == 'coprime':
if len(invariants) == 3:
invariants = _reduce_invariants(invariants, [1,2,3])
elif len(invariants) == 4:
invariants = _reduce_invariants(invariants, [2,4,6,9])
A, B, C = invariants[0:3]
if K is None:
from sage.rings.fraction_field import FractionField
K = FractionField(A.parent())
if K.characteristic() in [2, 3, 5]:
raise NotImplementedError('no reconstruction of binary quintics '
'implemented for fields of characteristic 2, 3 or 5')
M = 2*A*B - 3*C
N = K(2)**-1 * (A*C-B**2)
R2 = -K(2)**-1 * (A*N**2-2*B*M*N+C*M**2)
scale = [1,1,1,1,1,1]
from sage.functions.all import binomial, sqrt
if len(invariants) == 3:
if R2.is_square():
R = sqrt(R2)
else:
# if R2 is not a square, we scale the invariants in a suitable way
# so that the 'new' R2 is a square
[A, B, C] = [R2*A, R2**2*B, R2**3*C]
[M, N] = [R2**3*M, R2**4*N]
R = R2**5
elif len(invariants) == 4:
if invariants[3]**2 != R2:
raise ValueError('provided invariants do not satisfy the syzygy '
'for Clebsch invariants of a binary quintic')
R = invariants[3]
else:
raise ValueError('incorrect number of invariants provided, this '
'method requires 3 or 4 invariants')
if M == 0:
if N == 0:
if A == 0:
raise ValueError('no unique reconstruction possible for '
'quintics with a treefold linear factor')
else:
if B == 0:
return (1,0,0,0,0,1)
else:
return (0,1,0,0,1,0)
else:
# case corresponding to using alpha and gamma as coordinates
if A == 0:
return (1,0,0,0,1,0)
else:
if scaling == 'normalized':
# scaling z by (R/A**3)
scale = [ (-N)**-5*A**6*(R/A**3)**i for i in range(6) ]
D = -N
Delta = C
a = [0]
a.append((2*K(3)**-1*A**2-B)*N*B*K(2)**-1 - N**2*K(2)**-1)
B0 = 2*K(3)**-1*A*R
B1 = A*N*B*K(3)**-1
C0 = 2*K(3)**-1*R
C1 = B*N
else:
# case corresponding to using alpha and beta as coordinates
if R == 0:
if A == 0:
return (1,0,10,0,-15,0)
elif scaling == 'normalized':
# scaling x by A and z by sqrt(A)
scale = [ (-M)**(-5)*sqrt(A)**(12+i) for i in range(6) ]
else:
if A == 0:
if B == 0:
return (1,0,0,1,0,0)
elif scaling == 'normalized':
# scaling y by R/B**2
scale = [ (-M)**(-3)*(R/B**2)**i for i in range(6) ]
elif scaling == 'normalized':
# scaling y by R/A**4
scale = [ (-M)**(-3)*(R/A**4)**i for i in range(6) ]
D = -M
Delta = A
a = [0]
a.append((2*K(3)**-1*A**2-B)*(N*A-M*B)*K(2)**-1 \
- M*(N*K(2)**-1-M*A*K(3)**-1))
B0 = R
B1 = K(2)**-1*(N*A-M*B)
C0 = 0
C1 = -M
a[0] = (2*K(3)**-1*A**2-B)*R
a.append(-D*B0 - K(2)**-1*Delta*a[0])
a.append(-D*B1 - K(2)**-1*Delta*a[1])
a.append(D**2*C0 + D*Delta*B0 + K(4)**-1*Delta**2*a[0])
a.append(D**2*C1 + D*Delta*B1 + K(4)**-1*Delta**2*a[1])
coeffs = tuple([K((-1)**i*binomial(5,i)*scale[5-i]*a[i]) for i in range(6)])
if scaling == 'coprime':
from sage.arith.misc import gcd
return tuple([coeffs[i]/gcd(coeffs) for i in range(6)])
else:
return coeffs
def basis(self, reduce=True):
r"""
Produce a basis for the free abelian group of eta-products of level
N (under multiplication), attempting to find basis vectors of the
smallest possible degree.
INPUT:
- ``reduce`` - a boolean (default True) indicating
whether or not to apply LLL-reduction to the calculated basis
EXAMPLES::
sage: EtaGroup(5).basis()
[Eta product of level 5 : (eta_1)^6 (eta_5)^-6]
sage: EtaGroup(12).basis()
[Eta product of level 12 : (eta_1)^-3 (eta_2)^2 (eta_3)^1 (eta_4)^-1 (eta_6)^-2 (eta_12)^3,
Eta product of level 12 : (eta_1)^-4 (eta_2)^2 (eta_3)^4 (eta_6)^-2,
Eta product of level 12 : (eta_1)^6 (eta_2)^-9 (eta_3)^-2 (eta_4)^3 (eta_6)^3 (eta_12)^-1,
Eta product of level 12 : (eta_1)^-1 (eta_2)^3 (eta_3)^3 (eta_4)^-2 (eta_6)^-9 (eta_12)^6,
Eta product of level 12 : (eta_1)^3 (eta_3)^-1 (eta_4)^-3 (eta_12)^1]
sage: EtaGroup(12).basis(reduce=False) # much bigger coefficients
[Eta product of level 12 : (eta_1)^384 (eta_2)^-576 (eta_3)^-696 (eta_4)^216 (eta_6)^576 (eta_12)^96,
Eta product of level 12 : (eta_2)^24 (eta_12)^-24,
Eta product of level 12 : (eta_1)^-40 (eta_2)^116 (eta_3)^96 (eta_4)^-30 (eta_6)^-80 (eta_12)^-62,
Eta product of level 12 : (eta_1)^-4 (eta_2)^-33 (eta_3)^-4 (eta_4)^1 (eta_6)^3 (eta_12)^37,
Eta product of level 12 : (eta_1)^15 (eta_2)^-24 (eta_3)^-29 (eta_4)^9 (eta_6)^24 (eta_12)^5]
ALGORITHM: An eta product of level `N` is uniquely
determined by the integers `r_d` for `d | N` with
`d < N`, since `\sum_{d | N} r_d = 0`. The valid
`r_d` are those that satisfy two congruences modulo 24,
and one congruence modulo 2 for every prime divisor of N. We beef
up the congruences modulo 2 to congruences modulo 24 by multiplying
by 12. To calculate the kernel of the ensuing map
`\ZZ^m \to (\ZZ/24\ZZ)^n`
we lift it arbitrarily to an integer matrix and calculate its Smith
normal form. This gives a basis for the lattice.
This lattice typically contains "large" elements, so by default we
pass it to the reduce_basis() function which performs
LLL-reduction to give a more manageable basis.
"""
N = self.level()
divs = divisors(N)[:-1]
s = len(divs)
primedivs = prime_divisors(N)
rows = []
for di in divs:
# generate a row of relation matrix
row = [Mod(di, 24) - Mod(N, 24), Mod(N // di, 24) - Mod(1, 24)]
for p in primedivs:
row.append(Mod(12 * (N // di).valuation(p), 24))
rows.append(row)
M = matrix(IntegerModRing(24), rows)
Mlift = M.change_ring(ZZ)
# now we compute elementary factors of Mlift
S, U, V = Mlift.smith_form()
good_vects = []
for i in range(U.nrows()):
vect = U.row(i)
nf = (i < S.ncols() and S[i, i]) or 0 # ?
good_vects.append((vect * 24 / gcd(nf, 24)).list())
for v in good_vects:
v.append(-sum([r for r in v]))
dicts = []
for v in good_vects:
dicts.append({})
for i in range(s):
dicts[-1][divs[i]] = v[i]
dicts[-1][N] = v[-1]
if reduce:
return self.reduce_basis([self(d) for d in dicts])
else:
return [self(d) for d in dicts]
def prime_norm_representative(I, O, D, ell):
"""
Given an order O and a left O-ideal I return another
left O-ideal J in the same class, but with prime norm.
This corresponds to Step 1 in the notes. So given an ideal I it returns
an ideal in the same class but with reduced norm N where N != ell is
a large prime coprime to both D and p, and ell is a quadratic
nonresidue module N.
Args:
I: A left O-ideal.
O: An order in a quaternion algebra.
D: An integer.
ell: A prime.
Returns:
A pair (J, gamma) where J = I * gamma is a left O-ideal in the same
class with prime norm N. N will be coprime to both D and p, and ell
will be a nonquadratic residue module N.
"""
# TODO: Change so O is not an argument.
if not is_minkowski_basis(I.basis()):
print("Warning: The ideal I does not have a minkowski basis"
" precomputed and Sage can not do it for you.")
nrd_I = I.norm()
B = I.quaternion_algebra()
p = B.discriminant()
alpha = B(0)
normalized_norm = Integer(alpha.reduced_norm() / nrd_I)
# Choose random elements in I until one is found with norm N*nrd(I) where N
# is prime.
m_power = 3
m = Integer(2)**m_power # TODO: Change this to a proper bound.
count = 0
while (not is_prime(normalized_norm) or normalized_norm.divides(D)
or normalized_norm == ell or normalized_norm == p
or mod(ell, normalized_norm).is_square()):
# Make a new random element.
alpha = random_combination(I.basis(), bound=m)
normalized_norm = Integer(alpha.reduced_norm() / nrd_I)
# Increase the box we search in if we've been trying for too long. Note
# this was just a random heuristic I came up with, it's not in the
# paper.
count += 1
if count > 4 * m_power:
m_power += 1
m = Integer(2)**m_power
count = 0
# We now have an element alpha with norm N*nrd(I) where N is prime. The
# ideal J = I*gamma has prime norm where gamma = conjugate(alpha) / nrd(I).
gamma = alpha.conjugate() / nrd_I
J = I.scale(gamma)
assert is_prime(Integer(J.norm()))
assert not mod(ell, Integer(J.norm())).is_square()
assert gcd(Integer(J.norm()), D) == 1
return J, gamma
def __init__(self,
V,
W,
gens=None,
modulus=None,
modulus_qf=None,
check=True):
r"""
Initialize ``self``.
TESTS::
sage: from sage.modules.torsion_quadratic_module import TorsionQuadraticModule
sage: T = TorsionQuadraticModule(ZZ^3, 6*ZZ^3)
sage: TestSuite(T).run()
"""
if check:
if V.rank() != W.rank():
raise ValueError("modules must be of the same rank")
if V.base_ring() is not ZZ:
raise NotImplementedError("only currently implemented over ZZ")
if V.inner_product_matrix() != V.inner_product_matrix().transpose(
):
raise ValueError(
"the cover must have a symmetric inner product")
if gens is not None and V.span(gens) + W != V:
raise ValueError("provided gens do not generate the quotient")
FGP_Module_class.__init__(self, V, W, check=check)
if gens is None:
self._gens = FGP_Module_class.gens(self)
else:
self._gens = [self(v) for v in gens]
if modulus is not None:
if check:
# The inner product of two elements `b(v1+W,v2+W)` is defined `mod (V,W)`
num = gcd(
[x.inner_product(y) for x in V.gens() for y in W.gens()])
if num / modulus not in self.base_ring():
raise ValueError("the modulus must divide (V, W)")
self._modulus = modulus
else:
# The inner product of two elements `b(v1+W,v2+W)` is defined `mod (V,W)`
self._modulus = gcd(
[x.inner_product(y) for x in V.gens() for y in W.gens()])
if modulus_qf is not None:
if check:
# The quadratic_product of an element `q(v+W)` is defined
# `\mod 2(V,W) + ZZ\{ (w,w) | w in w\}`
norm = gcd(self.W().gram_matrix().diagonal())
num = gcd(norm, 2 * self._modulus)
if num / modulus_qf not in self.base_ring():
raise ValueError("the modulus_qf must divide (V, W)")
self._modulus_qf = modulus_qf
else:
# The quadratic_product of an element `q(v+W)` is defined
# `\mod 2(V,W) + ZZ\{ (w,w) | w in w\}`
norm = gcd(self.W().gram_matrix().diagonal())
self._modulus_qf = gcd(norm, 2 * self._modulus)
