def small_prime_value(self, Bmax=1000):
r"""
Returns a prime represented by this (primitive positive definite) binary form.
INPUT:
- ``Bmax`` -- a positive bound on the representing integers.
OUTPUT:
A prime number represented by the form.
.. note::
This is a very elementary implementation which just substitutes
values until a prime is found.
EXAMPLES::
sage: [Q.small_prime_value() for Q in BinaryQF_reduced_representatives(-23, primitive_only=True)]
[23, 2, 2]
sage: [Q.small_prime_value() for Q in BinaryQF_reduced_representatives(-47, primitive_only=True)]
[47, 2, 2, 3, 3]
"""
from sage.sets.all import Set
from sage.misc.all import srange
d = self.discriminant()
B = 10
while True:
llist = list(Set([self(x,y) for x in srange(-B,B) for y in srange(B)]))
llist = [l for l in llist if l.is_prime()]
llist.sort()
if llist:
return llist[0]
if B >= Bmax:
raise ValueError("Unable to find a prime value of %s" % self)
B += 10
def plot_fft(self, npoints=None, channel=0, half=True, **kwds):
v = self.vector(npoints=npoints)
w = v.fft()
if half:
w = w[:len(w) // 2]
z = [abs(x) for x in w]
if half:
r = math.pi
else:
r = 2 * math.pi
data = zip(srange(0, r, r / len(z)), z)
L = list_plot(data, plotjoined=True, **kwds)
L.xmin(0)
L.xmax(r)
return L
def plot_fft(self, npoints=None, channel=0, half=True, **kwds):
v = self.vector(npoints=npoints)
w = v.fft()
if half:
w = w[:len(w)//2]
z = [abs(x) for x in w]
if half:
r = math.pi
else:
r = 2*math.pi
data = zip(srange(0, r, r/len(z)), z)
L = list_plot(data, plotjoined=True, **kwds)
L.xmin(0)
L.xmax(r)
return L
def solve_integer(self, n):
r"""
Solve `Q(x,y) = n` in integers `x` and `y` where `Q` is this
quadratic form.
INPUT:
- ``Q`` (BinaryQF) -- a positive definite primitive integral
binary quadratic form
- ``n`` (int) -- a positive integer
OUTPUT:
A tuple (x,y) of integers satisfying `Q(x,y) = n` or ``None``
if no such `x` and `y` exist.
EXAMPLES::
sage: Qs = BinaryQF_reduced_representatives(-23,primitive_only=True)
sage: Qs
[x^2 + x*y + 6*y^2, 2*x^2 - x*y + 3*y^2, 2*x^2 + x*y + 3*y^2]
sage: [Q.solve_integer(3) for Q in Qs]
[None, (0, 1), (0, 1)]
sage: [Q.solve_integer(5) for Q in Qs]
[None, None, None]
sage: [Q.solve_integer(6) for Q in Qs]
[(0, 1), (-1, 1), (1, 1)]
"""
a, b, c = self
d = self.discriminant()
if d >= 0 or a <= 0:
raise ValueError("%s is not positive definite" % self)
ad = -d
an4 = 4*a*n
a2 = 2*a
from sage.misc.all import srange
for y in srange(0, 1+an4//ad):
z2 = an4 + d*y**2
for z in z2.sqrt(extend=False, all=True):
if a2.divides(z-b*y):
x = (z-b*y)//a2
return (x,y)
return None
def enum_projective_rational_field(X,B):
r"""
Enumerates projective, rational points on scheme ``X`` of height up to
bound ``B``.
INPUT:
- ``X`` - a scheme or set of abstract rational points of a scheme;
- ``B`` - a positive integer bound.
OUTPUT:
- a list containing the projective points of ``X`` of height up to ``B``,
sorted.
EXAMPLES::
sage: P.<X,Y,Z> = ProjectiveSpace(2,QQ)
sage: C = P.subscheme([X+Y-Z])
sage: from sage.schemes.projective.projective_rational_point import enum_projective_rational_field
sage: enum_projective_rational_field(C(QQ),6)
[(-5 : 6 : 1), (-4 : 5 : 1), (-3 : 4 : 1), (-2 : 3 : 1),
(-3/2 : 5/2 : 1), (-1 : 1 : 0), (-1 : 2 : 1), (-2/3 : 5/3 : 1),
(-1/2 : 3/2 : 1), (-1/3 : 4/3 : 1), (-1/4 : 5/4 : 1),
(-1/5 : 6/5 : 1), (0 : 1 : 1), (1/6 : 5/6 : 1), (1/5 : 4/5 : 1),
(1/4 : 3/4 : 1), (1/3 : 2/3 : 1), (2/5 : 3/5 : 1), (1/2 : 1/2 : 1),
(3/5 : 2/5 : 1), (2/3 : 1/3 : 1), (3/4 : 1/4 : 1), (4/5 : 1/5 : 1),
(5/6 : 1/6 : 1), (1 : 0 : 1), (6/5 : -1/5 : 1), (5/4 : -1/4 : 1),
(4/3 : -1/3 : 1), (3/2 : -1/2 : 1), (5/3 : -2/3 : 1), (2 : -1 : 1),
(5/2 : -3/2 : 1), (3 : -2 : 1), (4 : -3 : 1), (5 : -4 : 1),
(6 : -5 : 1)]
sage: enum_projective_rational_field(C,6) == enum_projective_rational_field(C(QQ),6)
True
::
sage: P3.<W,X,Y,Z> = ProjectiveSpace(3,QQ)
sage: enum_projective_rational_field(P3,1)
[(-1 : -1 : -1 : 1), (-1 : -1 : 0 : 1), (-1 : -1 : 1 : 0), (-1 : -1 : 1 : 1),
(-1 : 0 : -1 : 1), (-1 : 0 : 0 : 1), (-1 : 0 : 1 : 0), (-1 : 0 : 1 : 1),
(-1 : 1 : -1 : 1), (-1 : 1 : 0 : 0), (-1 : 1 : 0 : 1), (-1 : 1 : 1 : 0),
(-1 : 1 : 1 : 1), (0 : -1 : -1 : 1), (0 : -1 : 0 : 1), (0 : -1 : 1 : 0),
(0 : -1 : 1 : 1), (0 : 0 : -1 : 1), (0 : 0 : 0 : 1), (0 : 0 : 1 : 0),
(0 : 0 : 1 : 1), (0 : 1 : -1 : 1), (0 : 1 : 0 : 0), (0 : 1 : 0 : 1),
(0 : 1 : 1 : 0), (0 : 1 : 1 : 1), (1 : -1 : -1 : 1), (1 : -1 : 0 : 1),
(1 : -1 : 1 : 0), (1 : -1 : 1 : 1), (1 : 0 : -1 : 1), (1 : 0 : 0 : 0),
(1 : 0 : 0 : 1), (1 : 0 : 1 : 0), (1 : 0 : 1 : 1), (1 : 1 : -1 : 1),
(1 : 1 : 0 : 0), (1 : 1 : 0 : 1), (1 : 1 : 1 : 0), (1 : 1 : 1 : 1)]
ALGORITHM:
We just check all possible projective points in correct dimension
of projective space to see if they lie on ``X``.
AUTHORS:
- John Cremona and Charlie Turner (06-2010)
"""
from sage.schemes.projective.projective_space import is_ProjectiveSpace
if(is_Scheme(X)):
if (not is_ProjectiveSpace(X.ambient_space())):
raise TypeError("Ambient space must be projective space over the rational field")
X = X(X.base_ring())
else:
if (not is_ProjectiveSpace(X.codomain().ambient_space())):
raise TypeError("Codomain must be projective space over the rational field")
n = X.codomain().ambient_space().ngens()
zero = (0,) * n
pts = []
for c in cartesian_product_iterator([srange(-B,B+1) for _ in range(n)]):
if gcd(c) == 1 and c > zero:
try:
pts.append(X(c))
except TypeError:
pass
pts.sort()
return pts
def bsgs(a, b, bounds, operation='*', identity=None, inverse=None, op=None):
r"""
Totally generic discrete baby-step giant-step function.
Solves `na=b` (or `a^n=b`) with `lb\le n\le ub` where ``bounds==(lb,ub)``,
raising an error if no such `n` exists.
`a` and `b` must be elements of some group with given identity,
inverse of ``x`` given by ``inverse(x)``, and group operation on
``x``, ``y`` by ``op(x,y)``.
If operation is '*' or '+' then the other
arguments are provided automatically; otherwise they must be
provided by the caller.
INPUT:
- ``a`` - group element
- ``b`` - group element
- ``bounds`` - a 2-tuple of integers ``(lower,upper)`` with ``0<=lower<=upper``
- ``operation`` - string: '*', '+', 'other'
- ``identity`` - the identity element of the group
- ``inverse()`` - function of 1 argument ``x`` returning inverse of ``x``
- ``op()`` - function of 2 arguments ``x``, ``y`` returning ``x*y`` in group
OUTPUT:
An integer `n` such that `a^n = b` (or `na = b`). If no
such `n` exists, this function raises a ValueError exception.
NOTE: This is a generalization of discrete logarithm. One
situation where this version is useful is to find the order of
an element in a group where we only have bounds on the group
order (see the elliptic curve example below).
ALGORITHM: Baby step giant step. Time and space are soft
`O(\sqrt{n})` where `n` is the difference between upper and lower
bounds.
EXAMPLES::
sage: b = Mod(2,37); a = b^20
sage: bsgs(b, a, (0,36))
20
sage: p=next_prime(10^20)
sage: a=Mod(2,p); b=a^(10^25)
sage: bsgs(a, b, (10^25-10^6,10^25+10^6)) == 10^25
True
sage: K = GF(3^6,'b')
sage: a = K.gen()
sage: b = a^210
sage: bsgs(a, b, (0,K.order()-1))
210
sage: K.<z>=CyclotomicField(230)
sage: w=z^500
sage: bsgs(z,w,(0,229))
40
An additive example in an elliptic curve group::
sage: F.<a> = GF(37^5)
sage: E = EllipticCurve(F, [1,1])
sage: P = E.lift_x(a); P
(a : 28*a^4 + 15*a^3 + 14*a^2 + 7 : 1)
This will return a multiple of the order of P::
sage: bsgs(P,P.parent()(0),Hasse_bounds(F.order()),operation='+')
69327408
AUTHOR:
- John Cremona (2008-03-15)
"""
Z = integer_ring.ZZ
from operator import inv, mul, neg, add
if operation in multiplication_names:
identity = a.parent()(1)
inverse = inv
op = mul
elif operation in addition_names:
identity = a.parent()(0)
inverse = neg
op = add
else:
if identity is None or inverse is None or op is None:
raise ValueError("identity, inverse and operation must be given")
lb, ub = bounds
if lb < 0 or ub < lb:
raise ValueError("bsgs() requires 0<=lb<=ub")
if a.is_zero() and not b.is_zero():
raise ValueError("No solution in bsgs()")
ran = 1 + ub - lb # the length of the interval
c = op(inverse(b), multiple(a, lb, operation=operation))
if ran < 30: # use simple search for small ranges
i = lb
d = c
# for i,d in multiples(a,ran,c,indexed=True,operation=operation):
for i0 in range(ran):
i = lb + i0
if identity == d: # identity == b^(-1)*a^i, so return i
return Z(i)
d = op(a, d)
raise ValueError("No solution in bsgs()")
m = ran.isqrt() + 1 # we need sqrt(ran) rounded up
table = dict() # will hold pairs (a^(lb+i),lb+i) for i in range(m)
d = c
for i0 in misc.srange(m):
i = lb + i0
if identity == d: # identity == b^(-1)*a^i, so return i
return Z(i)
table[d] = i
d = op(d, a)
c = op(c, inverse(d)) # this is now a**(-m)
d = identity
for i in misc.srange(m):
j = table.get(d)
if j is not None: # then d == b*a**(-i*m) == a**j
return Z(i * m + j)
d = op(c, d)
raise ValueError("Log of %s to the base %s does not exist in %s." %
(b, a, bounds))
def enum_projective_rational_field(X, B):
r"""
Enumerates projective, rational points on scheme ``X`` of height up to
bound ``B``.
INPUT:
- ``X`` - a scheme or set of abstract rational points of a scheme;
- ``B`` - a positive integer bound.
OUTPUT:
- a list containing the projective points of ``X`` of height up to ``B``,
sorted.
EXAMPLES::
sage: P.<X,Y,Z> = ProjectiveSpace(2,QQ)
sage: C = P.subscheme([X+Y-Z])
sage: from sage.schemes.projective.projective_rational_point import enum_projective_rational_field
sage: enum_projective_rational_field(C(QQ),6)
[(-5 : 6 : 1), (-4 : 5 : 1), (-3 : 4 : 1), (-2 : 3 : 1),
(-3/2 : 5/2 : 1), (-1 : 1 : 0), (-1 : 2 : 1), (-2/3 : 5/3 : 1),
(-1/2 : 3/2 : 1), (-1/3 : 4/3 : 1), (-1/4 : 5/4 : 1),
(-1/5 : 6/5 : 1), (0 : 1 : 1), (1/6 : 5/6 : 1), (1/5 : 4/5 : 1),
(1/4 : 3/4 : 1), (1/3 : 2/3 : 1), (2/5 : 3/5 : 1), (1/2 : 1/2 : 1),
(3/5 : 2/5 : 1), (2/3 : 1/3 : 1), (3/4 : 1/4 : 1), (4/5 : 1/5 : 1),
(5/6 : 1/6 : 1), (1 : 0 : 1), (6/5 : -1/5 : 1), (5/4 : -1/4 : 1),
(4/3 : -1/3 : 1), (3/2 : -1/2 : 1), (5/3 : -2/3 : 1), (2 : -1 : 1),
(5/2 : -3/2 : 1), (3 : -2 : 1), (4 : -3 : 1), (5 : -4 : 1),
(6 : -5 : 1)]
sage: enum_projective_rational_field(C,6) == enum_projective_rational_field(C(QQ),6)
True
::
sage: P3.<W,X,Y,Z> = ProjectiveSpace(3,QQ)
sage: enum_projective_rational_field(P3,1)
[(-1 : -1 : -1 : 1), (-1 : -1 : 0 : 1), (-1 : -1 : 1 : 0), (-1 : -1 : 1 : 1),
(-1 : 0 : -1 : 1), (-1 : 0 : 0 : 1), (-1 : 0 : 1 : 0), (-1 : 0 : 1 : 1),
(-1 : 1 : -1 : 1), (-1 : 1 : 0 : 0), (-1 : 1 : 0 : 1), (-1 : 1 : 1 : 0),
(-1 : 1 : 1 : 1), (0 : -1 : -1 : 1), (0 : -1 : 0 : 1), (0 : -1 : 1 : 0),
(0 : -1 : 1 : 1), (0 : 0 : -1 : 1), (0 : 0 : 0 : 1), (0 : 0 : 1 : 0),
(0 : 0 : 1 : 1), (0 : 1 : -1 : 1), (0 : 1 : 0 : 0), (0 : 1 : 0 : 1),
(0 : 1 : 1 : 0), (0 : 1 : 1 : 1), (1 : -1 : -1 : 1), (1 : -1 : 0 : 1),
(1 : -1 : 1 : 0), (1 : -1 : 1 : 1), (1 : 0 : -1 : 1), (1 : 0 : 0 : 0),
(1 : 0 : 0 : 1), (1 : 0 : 1 : 0), (1 : 0 : 1 : 1), (1 : 1 : -1 : 1),
(1 : 1 : 0 : 0), (1 : 1 : 0 : 1), (1 : 1 : 1 : 0), (1 : 1 : 1 : 1)]
ALGORITHM:
We just check all possible projective points in correct dimension
of projective space to see if they lie on ``X``.
AUTHORS:
- John Cremona and Charlie Turner (06-2010)
"""
if is_Scheme(X):
X = X(X.base_ring())
n = X.codomain().ambient_space().ngens()
zero = (0, ) * n
pts = []
for c in cartesian_product_iterator([srange(-B, B + 1) for _ in range(n)]):
if gcd(c) == 1 and c > zero:
try:
pts.append(X(c))
except TypeError:
pass
pts.sort()
return pts
def bsgs(a, b, bounds, operation='*', identity=None, inverse=None, op=None):
r"""
Totally generic discrete baby-step giant-step function.
Solves `na=b` (or `a^n=b`) with `lb\le n\le ub` where ``bounds==(lb,ub)``,
raising an error if no such `n` exists.
`a` and `b` must be elements of some group with given identity,
inverse of ``x`` given by ``inverse(x)``, and group operation on
``x``, ``y`` by ``op(x,y)``.
If operation is '*' or '+' then the other
arguments are provided automatically; otherwise they must be
provided by the caller.
INPUT:
- ``a`` - group element
- ``b`` - group element
- ``bounds`` - a 2-tuple of integers ``(lower,upper)`` with ``0<=lower<=upper``
- ``operation`` - string: '*', '+', 'other'
- ``identity`` - the identity element of the group
- ``inverse()`` - function of 1 argument ``x`` returning inverse of ``x``
- ``op()`` - function of 2 arguments ``x``, ``y`` returning ``x*y`` in group
OUTPUT:
An integer `n` such that `a^n = b` (or `na = b`). If no
such `n` exists, this function raises a ValueError exception.
NOTE: This is a generalization of discrete logarithm. One
situation where this version is useful is to find the order of
an element in a group where we only have bounds on the group
order (see the elliptic curve example below).
ALGORITHM: Baby step giant step. Time and space are soft
`O(\sqrt{n})` where `n` is the difference between upper and lower
bounds.
EXAMPLES::
sage: b = Mod(2,37); a = b^20
sage: bsgs(b, a, (0,36))
20
sage: p=next_prime(10^20)
sage: a=Mod(2,p); b=a^(10^25)
sage: bsgs(a, b, (10^25-10^6,10^25+10^6)) == 10^25
True
sage: K = GF(3^6,'b')
sage: a = K.gen()
sage: b = a^210
sage: bsgs(a, b, (0,K.order()-1))
210
sage: K.<z>=CyclotomicField(230)
sage: w=z^500
sage: bsgs(z,w,(0,229))
40
An additive example in an elliptic curve group::
sage: F.<a> = GF(37^5)
sage: E = EllipticCurve(F, [1,1])
sage: P = E.lift_x(a); P
(a : 28*a^4 + 15*a^3 + 14*a^2 + 7 : 1)
This will return a multiple of the order of P::
sage: bsgs(P,P.parent()(0),Hasse_bounds(F.order()),operation='+')
69327408
AUTHOR:
- John Cremona (2008-03-15)
"""
Z = integer_ring.ZZ
from operator import inv, mul, neg, add
if operation in multiplication_names:
identity = a.parent()(1)
inverse = inv
op = mul
elif operation in addition_names:
identity = a.parent()(0)
inverse = neg
op = add
else:
if identity is None or inverse is None or op is None:
raise ValueError("identity, inverse and operation must be given")
lb, ub = bounds
if lb<0 or ub<lb:
raise ValueError("bsgs() requires 0<=lb<=ub")
if a.is_zero() and not b.is_zero():
raise ValueError("No solution in bsgs()")
ran = 1 + ub - lb # the length of the interval
c = op(inverse(b),multiple(a,lb,operation=operation))
if ran < 30: # use simple search for small ranges
i = lb
d = c
# for i,d in multiples(a,ran,c,indexed=True,operation=operation):
for i0 in range(ran):
i = lb + i0
if identity == d: # identity == b^(-1)*a^i, so return i
return Z(i)
d = op(a,d)
raise ValueError("No solution in bsgs()")
m = ran.isqrt()+1 # we need sqrt(ran) rounded up
table = dict() # will hold pairs (a^(lb+i),lb+i) for i in range(m)
d=c
for i0 in misc.srange(m):
i = lb + i0
if identity==d: # identity == b^(-1)*a^i, so return i
return Z(i)
table[d] = i
d=op(d,a)
c = op(c,inverse(d)) # this is now a**(-m)
d=identity
for i in misc.srange(m):
j = table.get(d)
if j is not None: # then d == b*a**(-i*m) == a**j
return Z(i*m + j)
d=op(c,d)
raise ValueError("Log of %s to the base %s does not exist in %s."%(b,a,bounds))
