def number_field_elements_from_algebraics(elts, name='a'):
r"""
The native Sage function ``number_field_elements_from_algebraics`` currently
returns number field *without* embedding. This function return field with
embedding!
EXAMPLES::
sage: from flatsurf.geometry.subfield import number_field_elements_from_algebraics
sage: z = QQbar.zeta(5)
sage: c = z.real()
sage: s = z.imag()
sage: number_field_elements_from_algebraics((c,s))
(Number Field in a with defining polynomial y^4 - 5*y^2 + 5 with a = 1.902113032590308?,
[1/2*a^2 - 3/2, 1/2*a])
sage: number_field_elements_from_algebraics([AA(1), AA(2/3)])
(Rational Field, [1, 2/3])
"""
# case when all elements are rationals
if all(x in QQ for x in elts):
return QQ, [QQ(x) for x in elts]
# general case
from sage.rings.qqbar import number_field_elements_from_algebraics
field, elts, phi = number_field_elements_from_algebraics(elts,
minimal=True)
polys = [x.polynomial() for x in elts]
K = NumberField(field.polynomial(), name, embedding=AA(phi(field.gen())))
gen = K.gen()
return K, [x.polynomial()(gen) for x in elts]
def __init__(self,lambda_squared=None, field=None):
if lambda_squared==None:
from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
R=PolynomialRing(ZZ,'x')
x = R.gen()
field=NumberField(x**3-ZZ(5)*x**2+ZZ(4)*x-ZZ(1), 'r', embedding=AA(ZZ(4)))
self._l=field.gen()
else:
if field is None:
self._l=lambda_squared
field=lambda_squared.parent()
else:
self._l=field(lambda_squared)
Surface.__init__(self,field, ZZ.zero(), finite=False)
def __init__(self, lambda_squared=None, field=None):
if lambda_squared == None:
from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
R = PolynomialRing(ZZ, 'x')
x = R.gen()
field = NumberField(x**3 - ZZ(5) * x**2 + ZZ(4) * x - ZZ(1),
'r',
embedding=AA(ZZ(4)))
self._l = field.gen()
else:
if field is None:
self._l = lambda_squared
field = lambda_squared.parent()
else:
self._l = field(lambda_squared)
Surface.__init__(self, field, ZZ.zero(), finite=False)
def is_cm_j_invariant(j, method='new'):
"""
Return whether or not this is a CM `j`-invariant.
INPUT:
- ``j`` -- an element of a number field `K`
OUTPUT:
A pair (bool, (d,f)) which is either (False, None) if `j` is not a
CM j-invariant or (True, (d,f)) if `j` is the `j`-invariant of the
imaginary quadratic order of discriminant `D=df^2` where `d` is
the associated fundamental discriminant and `f` the index.
.. note::
The current implementation makes use of the classification of
all orders of class number up to 100, and hence will raise an
error if `j` is an algebraic integer of degree greater than
this. It would be possible to implement a more general
version, using the fact that `d` must be supported on the
primes dividing the discriminant of the minimal polynomial of
`j`.
EXAMPLES::
sage: from sage.schemes.elliptic_curves.cm import is_cm_j_invariant
sage: is_cm_j_invariant(0)
(True, (-3, 1))
sage: is_cm_j_invariant(8000)
(True, (-8, 1))
sage: K.<a> = QuadraticField(5)
sage: is_cm_j_invariant(282880*a + 632000)
(True, (-20, 1))
sage: K.<a> = NumberField(x^3 - 2)
sage: is_cm_j_invariant(31710790944000*a^2 + 39953093016000*a + 50337742902000)
(True, (-3, 6))
TESTS::
sage: from sage.schemes.elliptic_curves.cm import is_cm_j_invariant
sage: all([is_cm_j_invariant(j) == (True, (d,f)) for d,f,j in cm_j_invariants_and_orders(QQ)])
True
"""
# First we check that j is an algebraic number:
from sage.rings.all import NumberFieldElement, NumberField
if not isinstance(j, NumberFieldElement) and not j in QQ:
raise NotImplementedError(
"is_cm_j_invariant() is only implemented for number field elements"
)
# for j in ZZ we have a lookup-table:
if j in ZZ:
j = ZZ(j)
table = dict([(jj, (d, f))
for d, f, jj in cm_j_invariants_and_orders(QQ)])
if j in table:
return True, table[j]
return False, None
# Otherwise if j is in Q then it is not integral so is not CM:
if j in QQ:
return False, None
# Now j has degree at least 2. If it is not integral so is not CM:
if not j.is_integral():
return False, None
# Next we find its minimal polynomial and degree h, and if h is
# less than the degree of j.parent() we recreate j as an element
# of Q(j):
jpol = PolynomialRing(QQ, 'x')([-j, 1
]) if j in QQ else j.absolute_minpoly()
h = jpol.degree()
# This will be used as a fall-back if we cannot determine the
# result using local data. For this to be necessary there would
# have to be very few primes of degree 1 and norm under 1000,
# since we only need to find one prime of degree 1, good
# reduction for which a_P is nonzero.
if method == 'old':
if h > 100:
raise NotImplementedError(
"CM data only available for class numbers up to 100")
for d, f in cm_orders(h):
if jpol == hilbert_class_polynomial(d * f**2):
return True, (d, f)
return False, None
# replace j by a clone whose parent is Q(j), if necessary:
K = j.parent()
if h < K.absolute_degree():
K = NumberField(jpol, 'j')
j = K.gen()
# Construct an elliptic curve with j-invariant j, with
# integral model:
from sage.schemes.elliptic_curves.all import EllipticCurve
E = EllipticCurve(j=j).integral_model()
D = E.discriminant()
prime_bound = 1000 # test primes of degree 1 up to this norm
max_primes = 20 # test at most this many primes
num_prime = 0
cmd = 0
cmf = 0
# Test primes of good reduction. If E has CM then for half the
# primes P we will have a_P=0, and for all other prime P the CM
# field is Q(sqrt(a_P^2-4N(P))). Hence if these fields are
# different for two primes then E does not have CM. If they are
# all equal for the primes tested, then we have a candidate CM
# field. Moreover the discriminant of the endomorphism ring
# divides all the values a_P^2-4N(P), since that is the
# discriminant of the order containing the Frobenius at P. So we
# end up with a finite number (usually one) of candidate
# discriminants to test. Each is tested by checking that its class
# number is h, and if so then that j is a root of its Hilbert
# class polynomial. In practice non CM curves will be eliminated
# by the local test at a small number of primes (probably just 2).
for P in K.primes_of_degree_one_iter(prime_bound):
if num_prime > max_primes:
if cmd: # we have a candidate CM field already
break
else: # we need to try more primes
max_primes *= 2
if D.valuation(P) > 0: # skip bad primes
continue
aP = E.reduction(P).trace_of_frobenius()
if aP == 0: # skip supersingular primes
continue
num_prime += 1
DP = aP**2 - 4 * P.norm()
dP = DP.squarefree_part()
fP = ZZ(DP // dP).isqrt()
if cmd == 0: # first one, so store d and f
cmd = dP
cmf = fP
elif cmd != dP: # inconsistent with previous
return False, None
else: # consistent d, so update f
cmf = cmf.gcd(fP)
if cmd == 0: # no conclusion, we found no degree 1 primes, revert to old method
return is_cm_j_invariant(j, method='old')
# it looks like cm by disc cmd * f**2 where f divides cmf
if cmd % 4 != 1:
cmd = cmd * 4
cmf = cmf // 2
# Now we must check if h(cmd*f**2)==h for f|cmf; if so we check
# whether j is a root of the associated Hilbert class polynomial.
for f in cmf.divisors(): # only positive divisors
d = cmd * f**2
if h != d.class_number():
continue
pol = hilbert_class_polynomial(d)
if pol(j) == 0:
return True, (cmd, f)
return False, None
from sage.rings.all import NumberField, QQ R = QQ['x'] x = R.gen() F = NumberField(x * x - x - 1, 'a') a = F.gen()
def is_cm_j_invariant(j, method='new'):
"""
Return whether or not this is a CM `j`-invariant.
INPUT:
- ``j`` -- an element of a number field `K`
OUTPUT:
A pair (bool, (d,f)) which is either (False, None) if `j` is not a
CM j-invariant or (True, (d,f)) if `j` is the `j`-invariant of the
imaginary quadratic order of discriminant `D=df^2` where `d` is
the associated fundamental discriminant and `f` the index.
.. note::
The current implementation makes use of the classification of
all orders of class number up to 100, and hence will raise an
error if `j` is an algebraic integer of degree greater than
this. It would be possible to implement a more general
version, using the fact that `d` must be supported on the
primes dividing the discriminant of the minimal polynomial of
`j`.
EXAMPLES::
sage: from sage.schemes.elliptic_curves.cm import is_cm_j_invariant
sage: is_cm_j_invariant(0)
(True, (-3, 1))
sage: is_cm_j_invariant(8000)
(True, (-8, 1))
sage: K.<a> = QuadraticField(5)
sage: is_cm_j_invariant(282880*a + 632000)
(True, (-20, 1))
sage: K.<a> = NumberField(x^3 - 2)
sage: is_cm_j_invariant(31710790944000*a^2 + 39953093016000*a + 50337742902000)
(True, (-3, 6))
TESTS::
sage: from sage.schemes.elliptic_curves.cm import is_cm_j_invariant
sage: all([is_cm_j_invariant(j) == (True, (d,f)) for d,f,j in cm_j_invariants_and_orders(QQ)])
True
"""
# First we check that j is an algebraic number:
from sage.rings.all import NumberFieldElement, NumberField
if not isinstance(j, NumberFieldElement) and not j in QQ:
raise NotImplementedError("is_cm_j_invariant() is only implemented for number field elements")
# for j in ZZ we have a lookup-table:
if j in ZZ:
j = ZZ(j)
table = dict([(jj,(d,f)) for d,f,jj in cm_j_invariants_and_orders(QQ)])
if j in table:
return True, table[j]
return False, None
# Otherwise if j is in Q then it is not integral so is not CM:
if j in QQ:
return False, None
# Now j has degree at least 2. If it is not integral so is not CM:
if not j.is_integral():
return False, None
# Next we find its minimal polynomial and degree h, and if h is
# less than the degree of j.parent() we recreate j as an element
# of Q(j):
jpol = PolynomialRing(QQ,'x')([-j,1]) if j in QQ else j.absolute_minpoly()
h = jpol.degree()
# This will be used as a fall-back if we cannot determine the
# result using local data. For this to be necessary there would
# have to be very few primes of degree 1 and norm under 1000,
# since we only need to find one prime of degree 1, good
# reduction for which a_P is nonzero.
if method=='old':
if h>100:
raise NotImplementedError("CM data only available for class numbers up to 100")
for d,f in cm_orders(h):
if jpol == hilbert_class_polynomial(d*f**2):
return True, (d,f)
return False, None
# replace j by a clone whose parent is Q(j), if necessary:
K = j.parent()
if h < K.absolute_degree():
K = NumberField(jpol, 'j')
j = K.gen()
# Construct an elliptic curve with j-invariant j, with
# integral model:
from sage.schemes.elliptic_curves.all import EllipticCurve
E = EllipticCurve(j=j).integral_model()
D = E.discriminant()
prime_bound = 1000 # test primes of degree 1 up to this norm
max_primes = 20 # test at most this many primes
num_prime = 0
cmd = 0
cmf = 0
# Test primes of good reduction. If E has CM then for half the
# primes P we will have a_P=0, and for all other prime P the CM
# field is Q(sqrt(a_P^2-4N(P))). Hence if these fields are
# different for two primes then E does not have CM. If they are
# all equal for the primes tested, then we have a candidate CM
# field. Moreover the discriminant of the endomorphism ring
# divides all the values a_P^2-4N(P), since that is the
# discriminant of the order containing the Frobenius at P. So we
# end up with a finite number (usually one) of candidate
# discriminats to test. Each is tested by checking that its class
# number is h, and if so then that j is a root of its Hilbert
# class polynomial. In practice non CM curves will be eliminated
# by the local test at a small number of primes (probably just 2).
for P in K.primes_of_degree_one_iter(prime_bound):
if num_prime > max_primes:
if cmd: # we have a candidate CM field already
break
else: # we need to try more primes
max_primes *=2
if D.valuation(P)>0: # skip bad primes
continue
aP = E.reduction(P).trace_of_frobenius()
if aP == 0: # skip supersingular primes
continue
num_prime += 1
DP = aP**2 - 4*P.norm()
dP = DP.squarefree_part()
fP = ZZ(DP//dP).isqrt()
if cmd==0: # first one, so store d and f
cmd = dP
cmf = fP
elif cmd != dP: # inconsistent with previous
return False, None
else: # consistent d, so update f
cmf = cmf.gcd(fP)
if cmd==0: # no conclusion, we found no degree 1 primes, revert to old method
return is_cm_j_invariant(j, method='old')
# it looks like cm by disc cmd * f**2 where f divides cmf
if cmd%4!=1:
cmd = cmd*4
cmf = cmf//2
# Now we must check if h(cmd*f**2)==h for f|cmf; if so we check
# whether j is a root of the associated Hilbert class polynomial.
for f in cmf.divisors(): # only positive divisors
d = cmd*f**2
if h != d.class_number():
continue
pol = hilbert_class_polynomial(d)
if pol(j)==0:
return True, (cmd,f)
return False, None
def arnoux_yoccoz(genus):
r"""
Construct the Arnoux-Yoccoz surface of genus 3 or greater.
This presentation of the surface follows Section 2.3 of
Joshua P. Bowman's paper "The Complete Family of Arnoux-Yoccoz
Surfaces."
EXAMPLES::
sage: from flatsurf import *
sage: s = translation_surfaces.arnoux_yoccoz(4)
sage: TestSuite(s).run()
sage: s.is_delaunay_decomposed()
True
sage: s = s.canonicalize()
sage: field=s.base_ring()
sage: a = field.gen()
sage: from sage.matrix.constructor import Matrix
sage: m = Matrix([[a,0],[0,~a]])
sage: ss = m*s
sage: ss = ss.canonicalize()
sage: s.cmp_translation_surface(ss)==0
True
The Arnoux-Yoccoz pseudo-Anosov are known to have (minimal) invariant
foliations with SAF=0::
sage: S3 = translation_surfaces.arnoux_yoccoz(3)
sage: Jxx, Jyy, Jxy = S3.j_invariant()
sage: Jxx.is_zero() and Jyy.is_zero()
True
sage: Jxy
[ 0 2 0]
[ 2 -2 0]
[ 0 0 2]
sage: S4 = translation_surfaces.arnoux_yoccoz(4)
sage: Jxx, Jyy, Jxy = S4.j_invariant()
sage: Jxx.is_zero() and Jyy.is_zero()
True
sage: Jxy
[ 0 2 0 0]
[ 2 -2 0 0]
[ 0 0 2 2]
[ 0 0 2 0]
"""
g=ZZ(genus)
assert g>=3
from sage.rings.polynomial.polynomial_ring import polygen
x = polygen(AA)
p=sum([x**i for i in xrange(1,g+1)])-1
cp = AA.common_polynomial(p)
alpha_AA = AA.polynomial_root(cp, RIF(1/2, 1))
field=NumberField(alpha_AA.minpoly(),'alpha',embedding=alpha_AA)
a=field.gen()
from sage.modules.free_module import VectorSpace
V=VectorSpace(field,2)
p=[None for i in xrange(g+1)]
q=[None for i in xrange(g+1)]
p[0]=V(( (1-a**g)/2, a**2/(1-a) ))
q[0]=V(( -a**g/2, a ))
p[1]=V(( -(a**(g-1)+a**g)/2, (a-a**2+a**3)/(1-a) ))
p[g]=V(( 1+(a-a**g)/2, (3*a-1-a**2)/(1-a) ))
for i in xrange(2,g):
p[i]=V(( (a-a**i)/(1-a) , a/(1-a) ))
for i in xrange(1,g+1):
q[i]=V(( (2*a-a**i-a**(i+1))/(2*(1-a)), (a-a**(g-i+2))/(1-a) ))
from flatsurf.geometry.polygon import Polygons
P=Polygons(field)
s = Surface_list(field)
T = [None] * (2*g+1)
Tp = [None] * (2*g+1)
from sage.matrix.constructor import Matrix
m=Matrix([[1,0],[0,-1]])
for i in xrange(1,g+1):
# T_i is (P_0,Q_i,Q_{i-1})
T[i]=s.add_polygon(P(edges=[ q[i]-p[0], q[i-1]-q[i], p[0]-q[i-1] ]))
# T_{g+i} is (P_i,Q_{i-1},Q_{i})
T[g+i]=s.add_polygon(P(edges=[ q[i-1]-p[i], q[i]-q[i-1], p[i]-q[i] ]))
# T'_i is (P'_0,Q'_{i-1},Q'_i)
Tp[i]=s.add_polygon(m*s.polygon(T[i]))
# T'_{g+i} is (P'_i,Q'_i, Q'_{i-1})
Tp[g+i]=s.add_polygon(m*s.polygon(T[g+i]))
for i in xrange(1,g):
s.change_edge_gluing(T[i],0,T[i+1],2)
s.change_edge_gluing(Tp[i],2,Tp[i+1],0)
for i in xrange(1,g+1):
s.change_edge_gluing(T[i],1,T[g+i],1)
s.change_edge_gluing(Tp[i],1,Tp[g+i],1)
#P 0 Q 0 is paired with P' 0 Q' 0, ...
s.change_edge_gluing(T[1],2,Tp[g],2)
s.change_edge_gluing(Tp[1],0,T[g],0)
# P1Q1 is paired with P'_g Q_{g-1}
s.change_edge_gluing(T[g+1],2,Tp[2*g],2)
s.change_edge_gluing(Tp[g+1],0,T[2*g],0)
# P1Q0 is paired with P_{g-1} Q_{g-1}
s.change_edge_gluing(T[g+1],0,T[2*g-1],2)
s.change_edge_gluing(Tp[g+1],2,Tp[2*g-1],0)
# PgQg is paired with Q1P2
s.change_edge_gluing(T[2*g],2,T[g+2],0)
s.change_edge_gluing(Tp[2*g],0,Tp[g+2],2)
for i in xrange(2,g-1):
# PiQi is paired with Q'_i P'_{i+1}
s.change_edge_gluing(T[g+i],2,Tp[g+i+1],2)
s.change_edge_gluing(Tp[g+i],0,T[g+i+1],0)
s.set_immutable()
return TranslationSurface(s)
from sage.rings.all import NumberField, QQ R = QQ['x'] x = R.gen() F = NumberField(x*x - x- 1, 'a') a = F.gen()
def mcmullen_genus2_prototype(w, h, t, e, rel=0):
r"""
McMullen prototypes in the stratum H(2).
These prototype appear at least in McMullen "Teichmüller curves in genus
two: Discriminant and spin" (2004). The notation from that paper are
quadruple ``(a, b, c, e)`` which translates in our notation as
``w = b``, ``h = c``, ``t = a`` (and ``e = e``).
The associated discriminant is `D = e^2 + 4 wh`.
If ``rel`` is a positive parameter (less than w-lambda) the surface belongs
to the eigenform locus in H(1,1).
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: from surface_dynamics import AbelianStratum
sage: prototypes = {
....: 5: [(1,1,0,-1)],
....: 8: [(1,1,0,-2), (2,1,0,0)],
....: 9: [(2,1,0,-1)],
....: 12: [(1,2,0,-2), (2,1,0,-2), (3,1,0,0)],
....: 13: [(1,1,0,-3), (3,1,0,-1), (3,1,0,1)],
....: 16: [(3,1,0,-2), (4,1,0,0)],
....: 17: [(1,2,0,-3), (2,1,0,-3), (2,2,0,-1), (2,2,1,-1), (4,1,0,-1), (4,1,0,1)],
....: 20: [(1,1,0,-4), (2,2,1,-2), (4,1,0,-2), (4,1,0,2)],
....: 21: [(1,3,0,-3), (3,1,0,-3)],
....: 24: [(1,2,0,-4), (2,1,0,-4), (3,2,0,0)],
....: 25: [(2,2,0,-3), (2,2,1,-3), (3,2,0,-1), (4,1,0,-3)]}
sage: for D in sorted(prototypes):
....: for w,h,t,e in prototypes[D]:
....: T = translation_surfaces.mcmullen_genus2_prototype(w,h,t,e)
....: assert T.stratum() == AbelianStratum(2)
....: assert (D.is_square() and T.base_ring() is QQ) or (T.base_ring().polynomial().discriminant() == D)
An example with some relative homology::
sage: U8 = translation_surfaces.mcmullen_genus2_prototype(2,1,0,0,1/4) # discriminant 8
sage: U12 = translation_surfaces.mcmullen_genus2_prototype(3,1,0,0,3/10) # discriminant 12
sage: U8.stratum()
H_2(1^2)
sage: U8.base_ring().polynomial().discriminant()
8
sage: U8.j_invariant()
(
[4 0]
(0), (0), [0 2]
)
sage: U12.stratum()
H_2(1^2)
sage: U12.base_ring().polynomial().discriminant()
12
sage: U12.j_invariant()
(
[6 0]
(0), (0), [0 2]
)
"""
w = ZZ(w)
h = ZZ(h)
t = ZZ(t)
e = ZZ(e)
g = w.gcd(h)
gg = g.gcd(t).gcd(e)
if w <= 0 or h <= 0 or t < 0 or t >= g or not g.gcd(t).gcd(
e).is_one() or e + h >= w:
raise ValueError("invalid parameters")
x = polygen(QQ)
poly = x**2 - e * x - w * h
if poly.is_irreducible():
emb = AA.polynomial_root(poly, RIF(0, w))
K = NumberField(poly, 'l', embedding=emb)
l = K.gen()
else:
K = QQ
D = e**2 + 4 * w * h
d = D.sqrt()
l = (e + d) / 2
rel = K(rel)
# (lambda,lambda) square on top
# twisted (w,0), (t,h)
s = Surface_list(base_ring=K)
if rel:
if rel < 0 or rel > w - l:
raise ValueError("invalid rel argument")
s.add_polygon(
polygons(vertices=[(0, 0), (l, 0), (l + rel, l), (rel, l)],
ring=K))
s.add_polygon(
polygons(vertices=[(0, 0), (rel, 0), (rel + l, 0), (w, 0),
(w + t, h), (l + rel + t, h), (t + l, h),
(t, h)],
ring=K))
s.set_edge_pairing(0, 1, 0, 3)
s.set_edge_pairing(0, 0, 1, 6)
s.set_edge_pairing(0, 2, 1, 1)
s.set_edge_pairing(1, 2, 1, 4)
s.set_edge_pairing(1, 3, 1, 7)
s.set_edge_pairing(1, 0, 1, 5)
else:
s.add_polygon(
polygons(vertices=[(0, 0), (l, 0), (l, l), (0, l)], ring=K))
s.add_polygon(
polygons(vertices=[(0, 0), (l, 0), (w, 0), (w + t, h),
(l + t, h), (t, h)],
ring=K))
s.set_edge_pairing(0, 1, 0, 3)
s.set_edge_pairing(0, 0, 1, 4)
s.set_edge_pairing(0, 2, 1, 0)
s.set_edge_pairing(1, 1, 1, 3)
s.set_edge_pairing(1, 2, 1, 5)
s.set_immutable()
return TranslationSurface(s)
def arnoux_yoccoz(genus):
r"""
Construct the Arnoux-Yoccoz surface of genus 3 or greater.
This presentation of the surface follows Section 2.3 of
Joshua P. Bowman's paper "The Complete Family of Arnoux-Yoccoz
Surfaces."
EXAMPLES::
sage: from flatsurf import *
sage: s = translation_surfaces.arnoux_yoccoz(4)
sage: TestSuite(s).run()
sage: s.is_delaunay_decomposed()
True
sage: s = s.canonicalize()
sage: field=s.base_ring()
sage: a = field.gen()
sage: from sage.matrix.constructor import Matrix
sage: m = Matrix([[a,0],[0,~a]])
sage: ss = m*s
sage: ss = ss.canonicalize()
sage: s.cmp(ss) == 0
True
The Arnoux-Yoccoz pseudo-Anosov are known to have (minimal) invariant
foliations with SAF=0::
sage: S3 = translation_surfaces.arnoux_yoccoz(3)
sage: Jxx, Jyy, Jxy = S3.j_invariant()
sage: Jxx.is_zero() and Jyy.is_zero()
True
sage: Jxy
[ 0 2 0]
[ 2 -2 0]
[ 0 0 2]
sage: S4 = translation_surfaces.arnoux_yoccoz(4)
sage: Jxx, Jyy, Jxy = S4.j_invariant()
sage: Jxx.is_zero() and Jyy.is_zero()
True
sage: Jxy
[ 0 2 0 0]
[ 2 -2 0 0]
[ 0 0 2 2]
[ 0 0 2 0]
"""
g = ZZ(genus)
assert g >= 3
x = polygen(AA)
p = sum([x**i for i in range(1, g + 1)]) - 1
cp = AA.common_polynomial(p)
alpha_AA = AA.polynomial_root(cp, RIF(1 / 2, 1))
field = NumberField(alpha_AA.minpoly(), 'alpha', embedding=alpha_AA)
a = field.gen()
V = VectorSpace(field, 2)
p = [None for i in range(g + 1)]
q = [None for i in range(g + 1)]
p[0] = V(((1 - a**g) / 2, a**2 / (1 - a)))
q[0] = V((-a**g / 2, a))
p[1] = V((-(a**(g - 1) + a**g) / 2, (a - a**2 + a**3) / (1 - a)))
p[g] = V((1 + (a - a**g) / 2, (3 * a - 1 - a**2) / (1 - a)))
for i in range(2, g):
p[i] = V(((a - a**i) / (1 - a), a / (1 - a)))
for i in range(1, g + 1):
q[i] = V(((2 * a - a**i - a**(i + 1)) / (2 * (1 - a)),
(a - a**(g - i + 2)) / (1 - a)))
P = ConvexPolygons(field)
s = Surface_list(field)
T = [None] * (2 * g + 1)
Tp = [None] * (2 * g + 1)
from sage.matrix.constructor import Matrix
m = Matrix([[1, 0], [0, -1]])
for i in range(1, g + 1):
# T_i is (P_0,Q_i,Q_{i-1})
T[i] = s.add_polygon(
P(edges=[q[i] - p[0], q[i - 1] - q[i], p[0] - q[i - 1]]))
# T_{g+i} is (P_i,Q_{i-1},Q_{i})
T[g + i] = s.add_polygon(
P(edges=[q[i - 1] - p[i], q[i] - q[i - 1], p[i] - q[i]]))
# T'_i is (P'_0,Q'_{i-1},Q'_i)
Tp[i] = s.add_polygon(m * s.polygon(T[i]))
# T'_{g+i} is (P'_i,Q'_i, Q'_{i-1})
Tp[g + i] = s.add_polygon(m * s.polygon(T[g + i]))
for i in range(1, g):
s.change_edge_gluing(T[i], 0, T[i + 1], 2)
s.change_edge_gluing(Tp[i], 2, Tp[i + 1], 0)
for i in range(1, g + 1):
s.change_edge_gluing(T[i], 1, T[g + i], 1)
s.change_edge_gluing(Tp[i], 1, Tp[g + i], 1)
#P 0 Q 0 is paired with P' 0 Q' 0, ...
s.change_edge_gluing(T[1], 2, Tp[g], 2)
s.change_edge_gluing(Tp[1], 0, T[g], 0)
# P1Q1 is paired with P'_g Q_{g-1}
s.change_edge_gluing(T[g + 1], 2, Tp[2 * g], 2)
s.change_edge_gluing(Tp[g + 1], 0, T[2 * g], 0)
# P1Q0 is paired with P_{g-1} Q_{g-1}
s.change_edge_gluing(T[g + 1], 0, T[2 * g - 1], 2)
s.change_edge_gluing(Tp[g + 1], 2, Tp[2 * g - 1], 0)
# PgQg is paired with Q1P2
s.change_edge_gluing(T[2 * g], 2, T[g + 2], 0)
s.change_edge_gluing(Tp[2 * g], 0, Tp[g + 2], 2)
for i in range(2, g - 1):
# PiQi is paired with Q'_i P'_{i+1}
s.change_edge_gluing(T[g + i], 2, Tp[g + i + 1], 2)
s.change_edge_gluing(Tp[g + i], 0, T[g + i + 1], 0)
s.set_immutable()
return TranslationSurface(s)