Computation of Frobenius matrix on Monsky-Washnitzer cohomology¶
The most interesting functions to be exported here are
matrix_of_frobenius()
and adjusted_prec()
.
Currently this code is limited to the case (no
for
), and only handles the
elliptic curve case (not more general hyperelliptic curves).
REFERENCES:
[Ked2001] | (1, 2) Kedlaya, K., “Counting points on hyperelliptic curves using Monsky-Washnitzer cohomology”, J. Ramanujan Math. Soc. 16 (2001) no 4, 323-338 |
[Edix] | Edixhoven, B., “Point counting after Kedlaya”, EIDMA-Stieltjes graduate course, Lieden (lecture notes?). |
AUTHORS:
- David Harvey and Robert Bradshaw: initial code developed at the 2006 MSRI graduate workshop, working with Jennifer Balakrishnan and Liang Xiao
- David Harvey (2006-08): cleaned up, rewrote some chunks, lots more documentation, added Newton iteration method, added more complete ‘trace trick’, integrated better into Sage.
- David Harvey (2007-02): added algorithm with sqrt(p) complexity (removed in May 2007 due to better C++ implementation)
- Robert Bradshaw (2007-03): keep track of exact form in reduction algorithms
- Robert Bradshaw (2007-04): generalization to hyperelliptic curves
- Julian Rueth (2014-05-09): improved caching
-
class
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
MonskyWashnitzerDifferential
(parent, val=0, offset=0)¶ Bases:
sage.structure.element.ModuleElement
Create an element of the Monsky-Washnitzer ring of differentials, of the form
.
INPUT:
parent
– Monsky-Washnitzer differential ring (instance of classMonskyWashnitzerDifferentialRing
val
– element of the base ring, or list of coefficientsoffset
– if non-zero, shift val by(default 0)
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5 - 4*x + 4) sage: x,y = C.monsky_washnitzer_gens() sage: MW = C.invariant_differential().parent() sage: sage.schemes.hyperelliptic_curves.monsky_washnitzer.MonskyWashnitzerDifferential(MW, x) x dx/2y sage: sage.schemes.hyperelliptic_curves.monsky_washnitzer.MonskyWashnitzerDifferential(MW, y) y*1 dx/2y sage: sage.schemes.hyperelliptic_curves.monsky_washnitzer.MonskyWashnitzerDifferential(MW, x, 10) y^10*x dx/2y
-
coeff
()¶ Returns
, where this element is
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: x,y = C.monsky_washnitzer_gens() sage: w = C.invariant_differential() sage: w 1 dx/2y sage: w.coeff() 1 sage: (x*y*w).coeff() y*x
-
coeffs
(R=None)¶ Used to obtain the raw coefficients of a differential, see
SpecialHyperellipticQuotientElement.coeffs()
INPUT:
- R – An (optional) base ring in which to cast the coefficients
OUTPUT:
The raw coefficients of
where self is
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: x,y = C.monsky_washnitzer_gens() sage: w = C.invariant_differential() sage: w.coeffs() ([(1, 0, 0, 0, 0)], 0) sage: (x*w).coeffs() ([(0, 1, 0, 0, 0)], 0) sage: (y*w).coeffs() ([(0, 0, 0, 0, 0), (1, 0, 0, 0, 0)], 0) sage: (y^-2*w).coeffs() ([(1, 0, 0, 0, 0), (0, 0, 0, 0, 0), (0, 0, 0, 0, 0)], -2)
-
coleman_integral
(P, Q)¶ Computes the definite integral of self from
to
.
INPUT:
- P, Q – Two points on the underlying curve
OUTPUT:
EXAMPLES:
sage: K = pAdicField(5,7) sage: E = EllipticCurve(K,[-31/3,-2501/108]) #11a sage: P = E(K(14/3), K(11/2)) sage: w = E.invariant_differential() sage: w.coleman_integral(P,2*P) O(5^6) sage: Q = E.lift_x(3) sage: w.coleman_integral(P,Q) 2*5 + 4*5^2 + 3*5^3 + 4*5^4 + 3*5^5 + O(5^6) sage: w.coleman_integral(2*P,Q) 2*5 + 4*5^2 + 3*5^3 + 4*5^4 + 3*5^5 + O(5^6) sage: (2*w).coleman_integral(P, Q) == 2*(w.coleman_integral(P, Q)) True
-
extract_pow_y
(k)¶ Returns the power of
in
where self is
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-3*x+1) sage: x,y = C.monsky_washnitzer_gens() sage: A = y^5 - x*y^3 sage: A.extract_pow_y(5) [1, 0, 0, 0, 0] sage: (A * C.invariant_differential()).extract_pow_y(5) [1, 0, 0, 0, 0]
-
integrate
(P, Q)¶ Computes the definite integral of self from
to
.
INPUT:
- P, Q – Two points on the underlying curve
OUTPUT:
EXAMPLES:
sage: K = pAdicField(5,7) sage: E = EllipticCurve(K,[-31/3,-2501/108]) #11a sage: P = E(K(14/3), K(11/2)) sage: w = E.invariant_differential() sage: w.coleman_integral(P,2*P) O(5^6) sage: Q = E.lift_x(3) sage: w.coleman_integral(P,Q) 2*5 + 4*5^2 + 3*5^3 + 4*5^4 + 3*5^5 + O(5^6) sage: w.coleman_integral(2*P,Q) 2*5 + 4*5^2 + 3*5^3 + 4*5^4 + 3*5^5 + O(5^6) sage: (2*w).coleman_integral(P, Q) == 2*(w.coleman_integral(P, Q)) True
-
max_pow_y
()¶ Returns the maximum power of
in
where self is
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-3*x+1) sage: x,y = C.monsky_washnitzer_gens() sage: w = y^5 * C.invariant_differential() sage: w.max_pow_y() 5 sage: w = (x^2*y^4 + y^5) * C.invariant_differential() sage: w.max_pow_y() 5
-
min_pow_y
()¶ Returns the minimum power of
in
where self is
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-3*x+1) sage: x,y = C.monsky_washnitzer_gens() sage: w = y^5 * C.invariant_differential() sage: w.min_pow_y() 5 sage: w = (x^2*y^4 + y^5) * C.invariant_differential() sage: w.min_pow_y() 4
-
reduce
()¶ Use homology relations to find
and
such that this element is equal to
, where
is given in terms of the
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: x,y = C.monsky_washnitzer_gens() sage: w = (y*x).diff() sage: w.reduce() (y*x, 0 dx/2y) sage: w = x^4 * C.invariant_differential() sage: w.reduce() (1/5*y*1, 4/5*1 dx/2y) sage: w = sum(QQ.random_element() * x^i * y^j for i in [0..4] for j in [-3..3]) * C.invariant_differential() sage: f, a = w.reduce() sage: f.diff() + a - w 0 dx/2y
-
reduce_fast
(even_degree_only=False)¶ Use homology relations to find
and
such that this element is equal to
, where
is given in terms of the
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^3-4*x+4) sage: x, y = E.monsky_washnitzer_gens() sage: x.diff().reduce_fast() (x, (0, 0)) sage: y.diff().reduce_fast() (y*1, (0, 0)) sage: (y^-1).diff().reduce_fast() ((y^-1)*1, (0, 0)) sage: (y^-11).diff().reduce_fast() ((y^-11)*1, (0, 0)) sage: (x*y^2).diff().reduce_fast() (y^2*x, (0, 0))
-
reduce_neg_y
()¶ Use homology relations to eliminate negative powers of
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-3*x+1) sage: x,y = C.monsky_washnitzer_gens() sage: (y^-1).diff().reduce_neg_y() ((y^-1)*1, 0 dx/2y) sage: (y^-5*x^2+y^-1*x).diff().reduce_neg_y() ((y^-1)*x + (y^-5)*x^2, 0 dx/2y)
-
reduce_neg_y_fast
(even_degree_only=False)¶ Use homology relations to eliminate negative powers of
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x, y = E.monsky_washnitzer_gens() sage: (y^-1).diff().reduce_neg_y_fast() ((y^-1)*1, 0 dx/2y) sage: (y^-5*x^2+y^-1*x).diff().reduce_neg_y_fast() ((y^-1)*x + (y^-5)*x^2, 0 dx/2y)
It leaves non-negative powers of
alone:
sage: y.diff() (-3*1 + 5*x^4) dx/2y sage: y.diff().reduce_neg_y_fast() (0, (-3*1 + 5*x^4) dx/2y)
-
reduce_neg_y_faster
(even_degree_only=False)¶ Use homology relations to eliminate negative powers of
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-3*x+1) sage: x,y = C.monsky_washnitzer_gens() sage: (y^-1).diff().reduce_neg_y() ((y^-1)*1, 0 dx/2y) sage: (y^-5*x^2+y^-1*x).diff().reduce_neg_y_faster() ((y^-1)*x + (y^-5)*x^2, 0 dx/2y)
-
reduce_pos_y
()¶ Use homology relations to eliminate positive powers of
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^3-4*x+4) sage: x,y = C.monsky_washnitzer_gens() sage: (y^2).diff().reduce_pos_y() (y^2*1, 0 dx/2y) sage: (y^2*x).diff().reduce_pos_y() (y^2*x, 0 dx/2y) sage: (y^92*x).diff().reduce_pos_y() (y^92*x, 0 dx/2y) sage: w = (y^3 + x).diff() sage: w += w.parent()(x) sage: w.reduce_pos_y_fast() (y^3*1 + x, x dx/2y)
-
reduce_pos_y_fast
(even_degree_only=False)¶ Use homology relations to eliminate positive powers of
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^3-4*x+4) sage: x, y = E.monsky_washnitzer_gens() sage: y.diff().reduce_pos_y_fast() (y*1, 0 dx/2y) sage: (y^2).diff().reduce_pos_y_fast() (y^2*1, 0 dx/2y) sage: (y^2*x).diff().reduce_pos_y_fast() (y^2*x, 0 dx/2y) sage: (y^92*x).diff().reduce_pos_y_fast() (y^92*x, 0 dx/2y) sage: w = (y^3 + x).diff() sage: w += w.parent()(x) sage: w.reduce_pos_y_fast() (y^3*1 + x, x dx/2y)
-
class
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
MonskyWashnitzerDifferentialRing
(base_ring)¶ Bases:
sage.structure.unique_representation.UniqueRepresentation
,sage.modules.module.Module
A ring of Monsky–Washnitzer differentials over
base_ring
.-
Q
()¶ Returns
where the model of the underlying hyperelliptic curve of self is given by
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: MW = C.invariant_differential().parent() sage: MW.Q() x^5 - 4*x + 4
-
base_extend
(R)¶ Return a new differential ring which is self base-extended to
INPUT:
R
– ring
OUTPUT:
Self, base-extended to
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: MW = C.invariant_differential().parent() sage: MW.base_ring() SpecialHyperellipticQuotientRing K[x,y,y^-1] / (y^2 = x^5 - 4*x + 4) over Rational Field sage: MW.base_extend(Qp(5,5)).base_ring() SpecialHyperellipticQuotientRing K[x,y,y^-1] / (y^2 = (1 + O(5^5))*x^5 + (1 + 4*5 + 4*5^2 + 4*5^3 + 4*5^4 + O(5^5))*x + (4 + O(5^5))) over 5-adic Field with capped relative precision 5
-
change_ring
(R)¶ Returns a new differential ring which is self with the coefficient ring changed to
.
INPUT:
R
– ring of coefficients
OUTPUT:
Self, with the coefficient ring changed to
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: MW = C.invariant_differential().parent() sage: MW.base_ring() SpecialHyperellipticQuotientRing K[x,y,y^-1] / (y^2 = x^5 - 4*x + 4) over Rational Field sage: MW.change_ring(Qp(5,5)).base_ring() SpecialHyperellipticQuotientRing K[x,y,y^-1] / (y^2 = (1 + O(5^5))*x^5 + (1 + 4*5 + 4*5^2 + 4*5^3 + 4*5^4 + O(5^5))*x + (4 + O(5^5))) over 5-adic Field with capped relative precision 5
-
degree
()¶ Returns the degree of
, where the model of the underlying hyperelliptic curve of self is given by
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: MW = C.invariant_differential().parent() sage: MW.Q() x^5 - 4*x + 4 sage: MW.degree() 5
-
dimension
()¶ Returns the dimension of self.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: K = Qp(7,5) sage: CK = C.change_ring(K) sage: MW = CK.invariant_differential().parent() sage: MW.dimension() 4
-
frob_Q
(p)¶ Returns and caches
, which is used in computing the image of
under a
-power lift of Frobenius to
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: MW = C.invariant_differential().parent() sage: MW.frob_Q(3) -(60-48*y^2+12*y^4-y^6)*1 + (192-96*y^2+12*y^4)*x - (192-48*y^2)*x^2 + 60*x^3 sage: MW.Q()(MW.x_to_p(3)) -(60-48*y^2+12*y^4-y^6)*1 + (192-96*y^2+12*y^4)*x - (192-48*y^2)*x^2 + 60*x^3 sage: MW.frob_Q(11) is MW.frob_Q(11) True
-
frob_basis_elements
(prec, p)¶ Returns the action of a
-power lift of Frobenius on the basis
where
is the degree of the underlying hyperelliptic curve.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: prec = 1 sage: p = 5 sage: MW = C.invariant_differential().parent() sage: MW.frob_basis_elements(prec,p) [((92000*y^-14-74200*y^-12+32000*y^-10-8000*y^-8+1000*y^-6-50*y^-4)*1 - (194400*y^-14-153600*y^-12+57600*y^-10-9600*y^-8+600*y^-6)*x + (204800*y^-14-153600*y^-12+38400*y^-10-3200*y^-8)*x^2 - (153600*y^-14-76800*y^-12+9600*y^-10)*x^3 + (63950*y^-14-18550*y^-12+1600*y^-10-400*y^-8+50*y^-6+5*y^-4)*x^4) dx/2y, (-(1391200*y^-14-941400*y^-12+302000*y^-10-76800*y^-8+14400*y^-6-1320*y^-4+30*y^-2)*1 + (2168800*y^-14-1402400*y^-12+537600*y^-10-134400*y^-8+16800*y^-6-720*y^-4)*x - (1596800*y^-14-1433600*y^-12+537600*y^-10-89600*y^-8+5600*y^-6)*x^2 + (1433600*y^-14-1075200*y^-12+268800*y^-10-22400*y^-8)*x^3 - (870200*y^-14-445350*y^-12+63350*y^-10-3200*y^-8+600*y^-6-30*y^-4-5*y^-2)*x^4) dx/2y, ((19488000*y^-14-15763200*y^-12+4944400*y^-10-913800*y^-8+156800*y^-6-22560*y^-4+1480*y^-2-10)*1 - (28163200*y^-14-18669600*y^-12+5774400*y^-10-1433600*y^-8+268800*y^-6-25440*y^-4+760*y^-2)*x + (15062400*y^-14-12940800*y^-12+5734400*y^-10-1433600*y^-8+179200*y^-6-8480*y^-4)*x^2 - (12121600*y^-14-11468800*y^-12+4300800*y^-10-716800*y^-8+44800*y^-6)*x^3 + (9215200*y^-14-6952400*y^-12+1773950*y^-10-165750*y^-8+5600*y^-6-720*y^-4+10*y^-2+5)*x^4) dx/2y, (-(225395200*y^-14-230640000*y^-12+91733600*y^-10-18347400*y^-8+2293600*y^-6-280960*y^-4+31520*y^-2-1480-10*y^2)*1 + (338048000*y^-14-277132800*y^-12+89928000*y^-10-17816000*y^-8+3225600*y^-6-472320*y^-4+34560*y^-2-720)*x - (172902400*y^-14-141504000*y^-12+58976000*y^-10-17203200*y^-8+3225600*y^-6-314880*y^-4+11520*y^-2)*x^2 + (108736000*y^-14-109760000*y^-12+51609600*y^-10-12902400*y^-8+1612800*y^-6-78720*y^-4)*x^3 - (85347200*y^-14-82900000*y^-12+31251400*y^-10-5304150*y^-8+367350*y^-6-8480*y^-4+760*y^-2+10-5*y^2)*x^4) dx/2y]
-
frob_invariant_differential
(prec, p)¶ Kedlaya’s algorithm allows us to calculate the action of Frobenius on the Monsky-Washnitzer cohomology. First we lift
to
by setting
Pulling back the differential
, we get
Use Newton’s method to calculate the square root.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: prec = 2 sage: p = 7 sage: MW = C.invariant_differential().parent() sage: MW.frob_invariant_differential(prec,p) ((67894400*y^-20-81198880*y^-18+40140800*y^-16-10035200*y^-14+1254400*y^-12-62720*y^-10)*1 - (119503944*y^-20-116064242*y^-18+43753472*y^-16-7426048*y^-14+514304*y^-12-12544*y^-10+1568*y^-8-70*y^-6-7*y^-4)*x + (78905288*y^-20-61014016*y^-18+16859136*y^-16-2207744*y^-14+250880*y^-12-37632*y^-10+3136*y^-8-70*y^-6)*x^2 - (39452448*y^-20-26148752*y^-18+8085490*y^-16-2007040*y^-14+376320*y^-12-37632*y^-10+1568*y^-8)*x^3 + (21102144*y^-20-18120592*y^-18+8028160*y^-16-2007040*y^-14+250880*y^-12-12544*y^-10)*x^4) dx/2y
-
helper_matrix
()¶ We use this to solve for the linear combination of
needed to clear all terms with
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: MW = C.invariant_differential().parent() sage: MW.helper_matrix() [ 256/2101 320/2101 400/2101 500/2101 625/2101] [-625/8404 -64/2101 -80/2101 -100/2101 -125/2101] [-125/2101 -625/8404 -64/2101 -80/2101 -100/2101] [-100/2101 -125/2101 -625/8404 -64/2101 -80/2101] [ -80/2101 -100/2101 -125/2101 -625/8404 -64/2101]
-
invariant_differential
()¶ Returns
as an element of self.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: MW = C.invariant_differential().parent() sage: MW.invariant_differential() 1 dx/2y
-
x_to_p
(p)¶ Returns and caches
, reduced via the relations coming from the defining polynomial of the hyperelliptic curve.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: C = HyperellipticCurve(x^5-4*x+4) sage: MW = C.invariant_differential().parent() sage: MW.x_to_p(3) x^3 sage: MW.x_to_p(5) -(4-y^2)*1 + 4*x sage: MW.x_to_p(101) is MW.x_to_p(101) True
-
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
MonskyWashnitzerDifferentialRing_class
¶ alias of
MonskyWashnitzerDifferentialRing
-
class
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
SpecialCubicQuotientRing
(Q, laurent_series=False)¶ Bases:
sage.rings.ring.CommutativeAlgebra
Specialised class for representing the quotient ring
, where
is an arbitrary commutative base ring (in which 2 and 3 are invertible),
and
are elements of that ring.
Polynomials are represented internally in the form
where the
are polynomials in
. Multiplication of polynomials always reduces high powers of
(i.e. beyond
) to powers of
.
Hopefully this ring is faster than a general quotient ring because it uses the special structure of this ring to speed multiplication (which is the dominant operation in the frobenius matrix calculation). I haven’t actually tested this theory though...
Todo
Eventually we will want to run this in characteristic 3, so we need to: (a) Allow
to contain an
term, and (b) Remove the requirement that 3 be invertible. Currently this is used in the Toom-Cook algorithm to speed multiplication.
EXAMPLES:
sage: B.<t> = PolynomialRing(Integers(125)) sage: R = monsky_washnitzer.SpecialCubicQuotientRing(t^3 - t + B(1/4)) sage: R SpecialCubicQuotientRing over Ring of integers modulo 125 with polynomial T = x^3 + 124*x + 94
Get generators:
sage: x, T = R.gens() sage: x (0) + (1)*x + (0)*x^2 sage: T (T) + (0)*x + (0)*x^2
Coercions:
sage: R(7) (7) + (0)*x + (0)*x^2
Create elements directly from polynomials:
sage: A = R.poly_ring() sage: A Univariate Polynomial Ring in T over Ring of integers modulo 125 sage: z = A.gen() sage: R.create_element(z^2, z+1, 3) (T^2) + (T + 1)*x + (3)*x^2
Some arithmetic:
sage: x^3 (T + 31) + (1)*x + (0)*x^2 sage: 3 * x**15 * T**2 + x - T (3*T^7 + 90*T^6 + 110*T^5 + 20*T^4 + 58*T^3 + 26*T^2 + 124*T) + (15*T^6 + 110*T^5 + 35*T^4 + 63*T^2 + 1)*x + (30*T^5 + 40*T^4 + 8*T^3 + 38*T^2)*x^2
Retrieve coefficients (output is zero-padded):
sage: x^10 (3*T^2 + 61*T + 8) + (T^3 + 93*T^2 + 12*T + 40)*x + (3*T^2 + 61*T + 9)*x^2 sage: (x^10).coeffs() [[8, 61, 3, 0], [40, 12, 93, 1], [9, 61, 3, 0]]
Todo
write an example checking multiplication of these polynomials against Sage’s ordinary quotient ring arithmetic. I can’t seem to get the quotient ring stuff happening right now...
-
create_element
(p0, p1, p2, check=True)¶ Creates the element
, where the
are polynomials in
.
INPUT:
p0, p1, p2
– coefficients; must be coercible- into poly_ring()
check
– bool (default True): whether to carry- out coercion
EXAMPLES:
sage: B.<t> = PolynomialRing(Integers(125)) sage: R = monsky_washnitzer.SpecialCubicQuotientRing(t^3 - t + B(1/4)) sage: A, z = R.poly_ring().objgen() sage: R.create_element(z^2, z+1, 3) (T^2) + (T + 1)*x + (3)*x^2
-
gens
()¶ Return a list [x, T] where x and T are the generators of the ring (as element of this ring).
Note
I have no idea if this is compatible with the usual Sage ‘gens’ interface.
EXAMPLES:
sage: B.<t> = PolynomialRing(Integers(125)) sage: R = monsky_washnitzer.SpecialCubicQuotientRing(t^3 - t + B(1/4)) sage: x, T = R.gens() sage: x (0) + (1)*x + (0)*x^2 sage: T (T) + (0)*x + (0)*x^2
-
poly_ring
()¶ Return the underlying polynomial ring in
.
EXAMPLES:
sage: B.<t> = PolynomialRing(Integers(125)) sage: R = monsky_washnitzer.SpecialCubicQuotientRing(t^3 - t + B(1/4)) sage: R.poly_ring() Univariate Polynomial Ring in T over Ring of integers modulo 125
-
-
class
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
SpecialCubicQuotientRingElement
(parent, p0, p1, p2, check=True)¶ Bases:
sage.structure.element.CommutativeAlgebraElement
An element of a SpecialCubicQuotientRing.
-
coeffs
()¶ Returns list of three lists of coefficients, corresponding to the
,
,
coefficients. The lists are zero padded to the same length. The list entries belong to the base ring.
EXAMPLES:
sage: B.<t> = PolynomialRing(Integers(125)) sage: R = monsky_washnitzer.SpecialCubicQuotientRing(t^3 - t + B(1/4)) sage: p = R.create_element(t, t^2 - 2, 3) sage: p.coeffs() [[0, 1, 0], [123, 0, 1], [3, 0, 0]]
-
scalar_multiply
(scalar)¶ Multiplies this element by a scalar, i.e. just multiply each coefficient of
by the scalar.
INPUT:
scalar
– either an element of base_ring, or an- element of poly_ring.
EXAMPLES:
sage: B.<t> = PolynomialRing(Integers(125)) sage: R = monsky_washnitzer.SpecialCubicQuotientRing(t^3 - t + B(1/4)) sage: x, T = R.gens() sage: f = R.create_element(2, t, t^2 - 3) sage: f (2) + (T)*x + (T^2 + 122)*x^2 sage: f.scalar_multiply(2) (4) + (2*T)*x + (2*T^2 + 119)*x^2 sage: f.scalar_multiply(t) (2*T) + (T^2)*x + (T^3 + 122*T)*x^2
-
shift
(n)¶ Returns this element multiplied by
.
EXAMPLES:
sage: B.<t> = PolynomialRing(Integers(125)) sage: R = monsky_washnitzer.SpecialCubicQuotientRing(t^3 - t + B(1/4)) sage: f = R.create_element(2, t, t^2 - 3) sage: f (2) + (T)*x + (T^2 + 122)*x^2 sage: f.shift(1) (2*T) + (T^2)*x + (T^3 + 122*T)*x^2 sage: f.shift(2) (2*T^2) + (T^3)*x + (T^4 + 122*T^2)*x^2
-
square
()¶ EXAMPLES:
sage: B.<t> = PolynomialRing(Integers(125)) sage: R = monsky_washnitzer.SpecialCubicQuotientRing(t^3 - t + B(1/4)) sage: x, T = R.gens()
sage: f = R.create_element(1 + 2*t + 3*t^2, 4 + 7*t + 9*t^2, 3 + 5*t + 11*t^2) sage: f.square() (73*T^5 + 16*T^4 + 38*T^3 + 39*T^2 + 70*T + 120) + (121*T^5 + 113*T^4 + 73*T^3 + 8*T^2 + 51*T + 61)*x + (18*T^4 + 60*T^3 + 22*T^2 + 108*T + 31)*x^2
-
-
class
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
SpecialHyperellipticQuotientElement
(parent, val=0, offset=0, check=True)¶ Bases:
sage.structure.element.CommutativeAlgebraElement
Elements in the Hyperelliptic quotient ring
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-36*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: MW = x.parent() sage: MW(x+x**2+y-77) # indirect doctest -(77-y)*1 + x + x^2
-
change_ring
(R)¶ Return the same element after changing the base ring to R
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-36*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: MW = x.parent() sage: z = MW(x+x**2+y-77) sage: z.change_ring(AA).parent() SpecialHyperellipticQuotientRing K[x,y,y^-1] / (y^2 = x^5 - 36*x + 1) over Algebraic Real Field
-
coeffs
(R=None)¶ Returns the raw coefficients of this element.
INPUT:
R
– an (optional) base-ring in which to cast the coefficients
OUTPUT:
coeffs
– a list of coefficients of powers offor each power
- of
n
– an offset indicating the power ofof the first list
- element
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.coeffs() ([(0, 1, 0, 0, 0)], 0) sage: y.coeffs() ([(0, 0, 0, 0, 0), (1, 0, 0, 0, 0)], 0) sage: a = sum(n*x^n for n in range(5)); a x + 2*x^2 + 3*x^3 + 4*x^4 sage: a.coeffs() ([(0, 1, 2, 3, 4)], 0) sage: a.coeffs(Qp(7)) ([(0, 1 + O(7^20), 2 + O(7^20), 3 + O(7^20), 4 + O(7^20))], 0) sage: (a*y).coeffs() ([(0, 0, 0, 0, 0), (0, 1, 2, 3, 4)], 0) sage: (a*y^-2).coeffs() ([(0, 1, 2, 3, 4), (0, 0, 0, 0, 0), (0, 0, 0, 0, 0)], -2)
Note that the coefficient list is transposed compared to how they are stored and printed:
sage: a*y^-2 (y^-2)*x + (2*y^-2)*x^2 + (3*y^-2)*x^3 + (4*y^-2)*x^4
A more complicated example:
sage: a = x^20*y^-3 - x^11*y^2; a (y^-3-4*y^-1+6*y-4*y^3+y^5)*1 - (12*y^-3-36*y^-1+36*y+y^2-12*y^3-2*y^4+y^6)*x + (54*y^-3-108*y^-1+54*y+6*y^2-6*y^4)*x^2 - (108*y^-3-108*y^-1+9*y^2)*x^3 + (81*y^-3)*x^4 sage: raw, offset = a.coeffs() sage: a.min_pow_y() -3 sage: offset -3 sage: raw [(1, -12, 54, -108, 81), (0, 0, 0, 0, 0), (-4, 36, -108, 108, 0), (0, 0, 0, 0, 0), (6, -36, 54, 0, 0), (0, -1, 6, -9, 0), (-4, 12, 0, 0, 0), (0, 2, -6, 0, 0), (1, 0, 0, 0, 0), (0, -1, 0, 0, 0)] sage: sum(c * x^i * y^(j+offset) for j, L in enumerate(raw) for i, c in enumerate(L)) == a True
Can also be used to construct elements:
sage: a.parent()(raw, offset) == a True
-
diff
()¶ Return the differential of
self
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: (x+3*y).diff() (-(9-2*y)*1 + 15*x^4) dx/2y
-
extract_pow_y
(k)¶ Return the coefficients of
in
self
as a listEXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: (x+3*y+9*x*y).extract_pow_y(1) [3, 9, 0, 0, 0]
-
max_pow_y
()¶ Return the maximal degree of
self
w.r.t. yEXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: (x+3*y).max_pow_y() 1
-
min_pow_y
()¶ Return the minimal degree of
self
w.r.t. yEXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: (x+3*y).min_pow_y() 0
-
truncate_neg
(n)¶ Return
self
minus its terms of degree less thanwrt
.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: (x+3*y+7*x*2*y**4).truncate_neg(1) 3*y*1 + 14*y^4*x
-
-
class
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
SpecialHyperellipticQuotientRing
(Q, R=None, invert_y=True)¶ Bases:
sage.structure.unique_representation.UniqueRepresentation
,sage.rings.ring.CommutativeAlgebra
Initialization.
TESTS:
Check that caching works:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: from sage.schemes.hyperelliptic_curves.monsky_washnitzer import SpecialHyperellipticQuotientRing sage: SpecialHyperellipticQuotientRing(E) is SpecialHyperellipticQuotientRing(E) True
-
Q
()¶ Return the defining polynomial of the underlying hyperelliptic curve.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-2*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().Q() x^5 - 2*x + 1
-
base_extend
(R)¶ Return the base extension of
self
to the ringR
if possible.EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().base_extend(UniversalCyclotomicField()) SpecialHyperellipticQuotientRing K[x,y,y^-1] / (y^2 = x^5 - 3*x + 1) over Universal Cyclotomic Field sage: x.parent().base_extend(ZZ) Traceback (most recent call last): ... TypeError: no such base extension
-
change_ring
(R)¶ Return the analog of
self
over the ringR
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().change_ring(ZZ) SpecialHyperellipticQuotientRing K[x,y,y^-1] / (y^2 = x^5 - 3*x + 1) over Integer Ring
-
curve
()¶ Return the underlying hyperelliptic curve.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().curve() Hyperelliptic Curve over Rational Field defined by y^2 = x^5 - 3*x + 1
-
degree
()¶ Return the degree of the underlying hyperelliptic curve.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().degree() 5
-
gens
()¶ Return the generators of
self
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().gens() (x, y*1)
-
is_field
(proof=True)¶ Return False as
self
is not a field.EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().is_field() False
-
monomial
(i, j, b=None)¶ Returns
, computed quickly.
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().monomial(4,5) y^5*x^4
-
monomial_diff_coeffs
(i, j)¶ The key here is that the formula for
is messy in terms of
, but varies nicely with
.
Where
have degree at most
for each
. Pre-compute
for each
the “hard” way, and the rest are easy.
-
monomial_diff_coeffs_matrices
()¶
-
monsky_washnitzer
()¶
-
prime
()¶
-
x
()¶ Return the generator
of
self
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().x() x
-
y
()¶ Return the generator
of
self
EXAMPLES:
sage: R.<x> = QQ['x'] sage: E = HyperellipticCurve(x^5-3*x+1) sage: x,y = E.monsky_washnitzer_gens() sage: x.parent().y() y*1
-
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
SpecialHyperellipticQuotientRing_class
¶ alias of
SpecialHyperellipticQuotientRing
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
adjusted_prec
(p, prec)¶ Computes how much precision is required in matrix_of_frobenius to get an answer correct to prec
-adic digits.
The issue is that the algorithm used in
matrix_of_frobenius()
sometimes performs divisions by, so precision is lost during the algorithm.
The estimate returned by this function is based on Kedlaya’s result (Lemmas 2 and 3 of [Ked2001]), which implies that if we start with
-adic digits, the total precision loss is at most
-adic digits. (This estimate is somewhat less than the amount you would expect by naively counting the number of divisions by
.)
INPUT:
p
– a prime = 5prec
– integer, desired output precision, = 1
OUTPUT: adjusted precision (usually slightly more than prec)
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
frobenius_expansion_by_newton
(Q, p, M)¶ Computes the action of Frobenius on
and on
, using Newton’s method (as suggested in Kedlaya’s paper [Ked2001]).
(This function does not yet use the cohomology relations - that happens afterwards in the “reduction” step.)
More specifically, it finds
and
in the quotient ring
, such that
where
(Here
is
, and
is the coefficient ring of
.)
and
are computed in the SpecialCubicQuotientRing associated to
, so all powers of
for
are reduced to powers of
.
INPUT:
Q
– cubic polynomial of the form, whose coefficient ring is a
-algebra
p
– residue characteristic of the p-adic fieldM
– p-adic precision of the coefficient ring- (this will be used to determine the number of Newton iterations)
OUTPUT:
F0, F1
- elements of SpecialCubicQuotientRing(Q), as described abover
- non-negative integer, as described above
EXAMPLES:
sage: from sage.schemes.hyperelliptic_curves.monsky_washnitzer import frobenius_expansion_by_newton sage: R.<x> = Integers(5^3)['x'] sage: Q = x^3 - x + R(1/4) sage: frobenius_expansion_by_newton(Q,5,3) ((25*T^5 + 75*T^3 + 100*T^2 + 100*T + 100) + (5*T^6 + 80*T^5 + 100*T^3 + 25*T + 50)*x + (55*T^5 + 50*T^4 + 75*T^3 + 25*T^2 + 25*T + 25)*x^2, (5*T^8 + 15*T^7 + 95*T^6 + 10*T^5 + 25*T^4 + 25*T^3 + 100*T^2 + 50) + (65*T^7 + 55*T^6 + 70*T^5 + 100*T^4 + 25*T^2 + 100*T)*x + (15*T^6 + 115*T^5 + 75*T^4 + 100*T^3 + 50*T^2 + 75*T + 75)*x^2, 7)
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
frobenius_expansion_by_series
(Q, p, M)¶ Computes the action of Frobenius on
and on
, using a series expansion.
(This function computes the same thing as frobenius_expansion_by_newton(), using a different method. Theoretically the Newton method should be asymptotically faster, when the precision gets large. However, in practice, this functions seems to be marginally faster for moderate precision, so I’m keeping it here until I figure out exactly why it is faster.)
(This function does not yet use the cohomology relations - that happens afterwards in the “reduction” step.)
More specifically, it finds F0 and F1 in the quotient ring
, such that
, and
where
. (Here
is
, and
is the coefficient ring of
.)
and
are computed in the SpecialCubicQuotientRing associated to
, so all powers of
for
are reduced to powers of
.
It uses the sum
and
INPUT:
Q
– cubic polynomial of the form, whose coefficient ring is a
-algebra
p
– residue characteristic of the-adic field
M
–-adic precision of the coefficient ring
- (this will be used to determine the number of terms in the series)
OUTPUT:
F0, F1
- elements of SpecialCubicQuotientRing(Q), as described abover
- non-negative integer, as described above
EXAMPLES:
sage: from sage.schemes.hyperelliptic_curves.monsky_washnitzer import frobenius_expansion_by_series sage: R.<x> = Integers(5^3)['x'] sage: Q = x^3 - x + R(1/4) sage: frobenius_expansion_by_series(Q,5,3) ((25*T^5 + 75*T^3 + 100*T^2 + 100*T + 100) + (5*T^6 + 80*T^5 + 100*T^3 + 25*T + 50)*x + (55*T^5 + 50*T^4 + 75*T^3 + 25*T^2 + 25*T + 25)*x^2, (5*T^8 + 15*T^7 + 95*T^6 + 10*T^5 + 25*T^4 + 25*T^3 + 100*T^2 + 50) + (65*T^7 + 55*T^6 + 70*T^5 + 100*T^4 + 25*T^2 + 100*T)*x + (15*T^6 + 115*T^5 + 75*T^4 + 100*T^3 + 50*T^2 + 75*T + 75)*x^2, 7)
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
helper_matrix
(Q)¶ Computes the (constant) matrix used to calculate the linear combinations of the
needed to eliminate the negative powers of
in the cohomology (i.e. in reduce_negative()).
INPUT:
Q
– cubic polynomial
EXAMPLES:
sage: t = polygen(QQ,'t') sage: from sage.schemes.hyperelliptic_curves.monsky_washnitzer import helper_matrix sage: helper_matrix(t**3-4*t-691) [ 64/12891731 -16584/12891731 4297329/12891731] [ 6219/12891731 -32/12891731 8292/12891731] [ -24/12891731 6219/12891731 -32/12891731]
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
lift
(x)¶ Tries to call x.lift(), presumably from the
-adics to ZZ.
If this fails, it assumes the input is a power series, and tries to lift it to a power series over QQ.
This function is just a very kludgy solution to the problem of trying to make the reduction code (below) work over both Zp and Zp[[t]].
EXAMPLES:
sage: from sage.schemes.hyperelliptic_curves.monsky_washnitzer import lift sage: l = lift(Qp(13)(131)); l 131 sage: l.parent() Integer Ring sage: x=PowerSeriesRing(Qp(17),'x').gen() sage: l = lift(4+5*x+17*x**6); l 4 + 5*t + 17*t^6 sage: l.parent() Power Series Ring in t over Rational Field
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
matrix_of_frobenius
(Q, p, M, trace=None, compute_exact_forms=False)¶ Computes the matrix of Frobenius on Monsky-Washnitzer cohomology, with respect to the basis
.
INPUT:
Q
– cubic polynomialdefining an elliptic curve
by
. The coefficient ring of
should be a
-algebra in which the matrix of frobenius will be constructed.
p
– prime = 5 for which E has good reductionM
– integer = 2;-adic precision of
the coefficient ring
trace
– (optional) the trace of the matrix, ifknown in advance. This is easy to compute because it is just the
of the curve. If the trace is supplied, matrix_of_frobenius will use it to speed the computation (i.e. we know the determinant is
, so we have two conditions, so really only column of the matrix needs to be computed. it is actually a little more complicated than that, but that’s the basic idea.) If trace=None, then both columns will be computed independently, and you can get a strong indication of correctness by verifying the trace afterwards.
Warning
THE RESULT WILL NOT NECESSARILY BE CORRECT TO M p-ADIC DIGITS. If you want prec digits of precision, you need to use the function adjusted_prec(), and then you need to reduce the answer mod
at the end.
OUTPUT:
2x2 matrix of frobenius on Monsky-Washnitzer cohomology, with entries in the coefficient ring of Q.
EXAMPLES:
A simple example:
sage: p = 5 sage: prec = 3 sage: M = monsky_washnitzer.adjusted_prec(p, prec) sage: M 5 sage: R.<x> = PolynomialRing(Integers(p**M)) sage: A = monsky_washnitzer.matrix_of_frobenius(x^3 - x + R(1/4), p, M) sage: A [3090 187] [2945 408]
But the result is only accurate to prec digits:
sage: B = A.change_ring(Integers(p**prec)) sage: B [90 62] [70 33]
Check trace (123 = -2 mod 125) and determinant:
sage: B.det() 5 sage: B.trace() 123 sage: EllipticCurve([-1, 1/4]).ap(5) -2
Try using the trace to speed up the calculation:
sage: A = monsky_washnitzer.matrix_of_frobenius(x^3 - x + R(1/4), ... p, M, -2) sage: A [2715 187] [1445 408]
Hmmm... it looks different, but that’s because the trace of our first answer was only -2 modulo
, not -2 modulo
. So the right answer is:
sage: A.change_ring(Integers(p**prec)) [90 62] [70 33]
Check it works with only one digit of precision:
sage: p = 5 sage: prec = 1 sage: M = monsky_washnitzer.adjusted_prec(p, prec) sage: R.<x> = PolynomialRing(Integers(p**M)) sage: A = monsky_washnitzer.matrix_of_frobenius(x^3 - x + R(1/4), p, M) sage: A.change_ring(Integers(p)) [0 2] [0 3]
Here is an example that is particularly badly conditioned for using the trace trick:
sage: p = 11 sage: prec = 3 sage: M = monsky_washnitzer.adjusted_prec(p, prec) sage: R.<x> = PolynomialRing(Integers(p**M)) sage: A = monsky_washnitzer.matrix_of_frobenius(x^3 + 7*x + 8, p, M) sage: A.change_ring(Integers(p**prec)) [1144 176] [ 847 185]
The problem here is that the top-right entry is divisible by 11, and the bottom-left entry is divisible by
. So when you apply the trace trick, neither
nor
is enough to compute the whole matrix to the desired precision, even if you try increasing the target precision by one. Nevertheless,
matrix_of_frobenius
knows how to get the right answer by evaluatinginstead:
sage: A = monsky_washnitzer.matrix_of_frobenius(x^3 + 7*x + 8, p, M, -2) sage: A.change_ring(Integers(p**prec)) [1144 176] [ 847 185]
The running time is about
O(p*prec**2)
(times some logarithmic factors), so it is feasible to run on fairly large primes, or precision (or both?!?!):sage: p = 10007 sage: prec = 2 sage: M = monsky_washnitzer.adjusted_prec(p, prec) sage: R.<x> = PolynomialRing(Integers(p**M)) sage: A = monsky_washnitzer.matrix_of_frobenius( # long time ... x^3 - x + R(1/4), p, M) # long time sage: B = A.change_ring(Integers(p**prec)); B # long time [74311982 57996908] [95877067 25828133] sage: B.det() # long time 10007 sage: B.trace() # long time 66 sage: EllipticCurve([-1, 1/4]).ap(10007) # long time 66
sage: p = 5 sage: prec = 300 sage: M = monsky_washnitzer.adjusted_prec(p, prec) sage: R.<x> = PolynomialRing(Integers(p**M)) sage: A = monsky_washnitzer.matrix_of_frobenius( # long time ... x^3 - x + R(1/4), p, M) # long time sage: B = A.change_ring(Integers(p**prec)) # long time sage: B.det() # long time 5 sage: -B.trace() # long time 2 sage: EllipticCurve([-1, 1/4]).ap(5) # long time -2
Let us check consistency of the results for a range of precisions:
sage: p = 5 sage: max_prec = 60 sage: M = monsky_washnitzer.adjusted_prec(p, max_prec) sage: R.<x> = PolynomialRing(Integers(p**M)) sage: A = monsky_washnitzer.matrix_of_frobenius(x^3 - x + R(1/4), p, M) # long time sage: A = A.change_ring(Integers(p**max_prec)) # long time sage: result = [] # long time sage: for prec in range(1, max_prec): # long time ... M = monsky_washnitzer.adjusted_prec(p, prec) # long time ... R.<x> = PolynomialRing(Integers(p^M),'x') # long time ... B = monsky_washnitzer.matrix_of_frobenius( # long time ... x^3 - x + R(1/4), p, M) # long time ... B = B.change_ring(Integers(p**prec)) # long time ... result.append(B == A.change_ring( # long time ... Integers(p**prec))) # long time sage: result == [True] * (max_prec - 1) # long time True
The remaining examples discuss what happens when you take the coefficient ring to be a power series ring; i.e. in effect you’re looking at a family of curves.
The code does in fact work...
sage: p = 11 sage: prec = 3 sage: M = monsky_washnitzer.adjusted_prec(p, prec) sage: S.<t> = PowerSeriesRing(Integers(p**M), default_prec=4) sage: a = 7 + t + 3*t^2 sage: b = 8 - 6*t + 17*t^2 sage: R.<x> = PolynomialRing(S) sage: Q = x**3 + a*x + b sage: A = monsky_washnitzer.matrix_of_frobenius(Q, p, M) # long time sage: B = A.change_ring(PowerSeriesRing(Integers(p**prec), 't', default_prec=4)) # long time sage: B # long time [1144 + 264*t + 841*t^2 + 1025*t^3 + O(t^4) 176 + 1052*t + 216*t^2 + 523*t^3 + O(t^4)] [ 847 + 668*t + 81*t^2 + 424*t^3 + O(t^4) 185 + 341*t + 171*t^2 + 642*t^3 + O(t^4)]
The trace trick should work for power series rings too, even in the badly- conditioned case. Unfortunately I don’t know how to compute the trace in advance, so I’m not sure exactly how this would help. Also, I suspect the running time will be dominated by the expansion, so the trace trick won’t really speed things up anyway. Another problem is that the determinant is not always p:
sage: B.det() # long time 11 + 484*t^2 + 451*t^3 + O(t^4)
However, it appears that the determinant always has the property that if you substitute t - 11t, you do get the constant series p (mod p**prec). Similarly for the trace. And since the parameter only really makes sense when it is divisible by p anyway, perhaps this isn’t a problem after all.
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
matrix_of_frobenius_hyperelliptic
(Q, p=None, prec=None, M=None)¶ Computes the matrix of Frobenius on Monsky-Washnitzer cohomology, with respect to the basis
, where
is the degree of
.
INPUT:
Q
– monic polynomialp
– primefor which
has good reduction
prec
– (optional)-adic precision of the coefficient ring
M
– (optional) adjusted-adic precision of the coefficint ring
OUTPUT:
x
matrix
of Frobenius on Monsky-Washnitzer cohomology, and list of differentials {f_i } such that
EXAMPLES:
sage: p = 5 sage: prec = 3 sage: R.<x> = QQ['x'] sage: A,f = monsky_washnitzer.matrix_of_frobenius_hyperelliptic(x^5 - 2*x + 3, p, prec) sage: A [ 4*5 + O(5^3) 5 + 2*5^2 + O(5^3) 2 + 3*5 + 2*5^2 + O(5^3) 2 + 5 + 5^2 + O(5^3)] [ 3*5 + 5^2 + O(5^3) 3*5 + O(5^3) 4*5 + O(5^3) 2 + 5^2 + O(5^3)] [ 4*5 + 4*5^2 + O(5^3) 3*5 + 2*5^2 + O(5^3) 5 + 3*5^2 + O(5^3) 2*5 + 2*5^2 + O(5^3)] [ 5^2 + O(5^3) 5 + 4*5^2 + O(5^3) 4*5 + 3*5^2 + O(5^3) 2*5 + O(5^3)]
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
reduce_all
(Q, p, coeffs, offset, compute_exact_form=False)¶ Applies cohomology relations to reduce all terms to a linear combination of
and
.
INPUT:
Q
– cubic polynomialcoeffs
– list of length 3 lists. Thelist [a, b, c] represents
.
offset
– nonnegative integer
OUTPUT:
A, B
- pair such that the input differential is cohomologous to (A + Bx) dx/y.
Note
The algorithm operates in-place, so the data in coeffs is destroyed.
EXAMPLE:
sage: R.<x> = Integers(5^3)['x'] sage: Q = x^3 - x + R(1/4) sage: coeffs = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] sage: coeffs = [[R.base_ring()(a) for a in row] for row in coeffs] sage: monsky_washnitzer.reduce_all(Q, 5, coeffs, 1) (21, 106)
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
reduce_negative
(Q, p, coeffs, offset, exact_form=None)¶ Applies cohomology relations to incorporate negative powers of
into the
term.
INPUT:
p
– primeQ
– cubic polynomialcoeffs
– list of length 3 lists. Thelist [a, b, c] represents
.
offset
– nonnegative integer
OUTPUT: The reduction is performed in-place. The output is placed in coeffs[offset]. Note that coeffs[i] will be meaningless for i offset after this function is finished.
EXAMPLE:
sage: R.<x> = Integers(5^3)['x'] sage: Q = x^3 - x + R(1/4) sage: coeffs = [[10, 15, 20], [1, 2, 3], [4, 5, 6], [7, 8, 9]] sage: coeffs = [[R.base_ring()(a) for a in row] for row in coeffs] sage: monsky_washnitzer.reduce_negative(Q, 5, coeffs, 3) sage: coeffs[3] [28, 52, 9]
sage: R.<x> = Integers(7^3)['x'] sage: Q = x^3 - x + R(1/4) sage: coeffs = [[7, 14, 21], [1, 2, 3], [4, 5, 6], [7, 8, 9]] sage: coeffs = [[R.base_ring()(a) for a in row] for row in coeffs] sage: monsky_washnitzer.reduce_negative(Q, 7, coeffs, 3) sage: coeffs[3] [245, 332, 9]
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
reduce_positive
(Q, p, coeffs, offset, exact_form=None)¶ Applies cohomology relations to incorporate positive powers of
into the
term.
INPUT:
Q
– cubic polynomialcoeffs
– list of length 3 lists. Thelist [a, b, c] represents
.
offset
– nonnegative integer
OUTPUT: The reduction is performed in-place. The output is placed in coeffs[offset]. Note that coeffs[i] will be meaningless for i offset after this function is finished.
EXAMPLE:
sage: R.<x> = Integers(5^3)['x'] sage: Q = x^3 - x + R(1/4)
sage: coeffs = [[1, 2, 3], [10, 15, 20]] sage: coeffs = [[R.base_ring()(a) for a in row] for row in coeffs] sage: monsky_washnitzer.reduce_positive(Q, 5, coeffs, 0) sage: coeffs[0] [16, 102, 88]
sage: coeffs = [[9, 8, 7], [10, 15, 20]] sage: coeffs = [[R.base_ring()(a) for a in row] for row in coeffs] sage: monsky_washnitzer.reduce_positive(Q, 5, coeffs, 0) sage: coeffs[0] [24, 108, 92]
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
reduce_zero
(Q, coeffs, offset, exact_form=None)¶ Applies cohomology relation to incorporate
term into
and
terms.
INPUT:
Q
– cubic polynomialcoeffs
– list of length 3 lists. Thelist [a, b, c] represents
.
offset
– nonnegative integer
OUTPUT: The reduction is performed in-place. The output is placed in coeffs[offset]. This method completely ignores coeffs[i] for i != offset.
EXAMPLE:
sage: R.<x> = Integers(5^3)['x'] sage: Q = x^3 - x + R(1/4) sage: coeffs = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] sage: coeffs = [[R.base_ring()(a) for a in row] for row in coeffs] sage: monsky_washnitzer.reduce_zero(Q, coeffs, 1) sage: coeffs[1] [6, 5, 0]
-
sage.schemes.hyperelliptic_curves.monsky_washnitzer.
transpose_list
(input)¶ INPUT:
input
– a list of lists, each list of the same- length
OUTPUT:
output
– a list of lists such that output[i][j]- = input[j][i]
EXAMPLES:
sage: from sage.schemes.hyperelliptic_curves.monsky_washnitzer import transpose_list sage: L = [[1, 2], [3, 4], [5, 6]] sage: transpose_list(L) [[1, 3, 5], [2, 4, 6]]