Completely multiplicative ideal weights #
The completely multiplicative specializations of TauCeti.IdealArithmeticFunction.
A TauCeti.MultiplicativeIdealWeight K is a monoid-with-zero homomorphism
Ideal (π K) β*β β killing only finitely many height-one primes, and
TauCeti.UnitaryIdealWeight K is the subtype of those whose values have modulus 1 away from
that finite bad set. Using Mathlib's β*β vocabulary is what pins the zero-ideal law
Ο β₯ = 0; the finiteness condition is what bounds the bad local factors of the Euler product.
Both carriers are degree one: the value at π ^ n is forced to be Ο π ^ n. They are
therefore deliberately too narrow for the ideal MΓΆbius function or for coefficient systems
whose prime-power values are independent local data; those get separate carriers.
The good ideals of a weight are the ideals prime to its bad primes in the sense of
Ideal.IsPrimeTo (from TauCeti.RingTheory.DedekindDomain.Ideal): nonzero and divisible by no
prime of the set. Its induction principle Ideal.IsPrimeTo.induction_on factors a good ideal
into good primes; this is the engine behind both
TauCeti.MultiplicativeIdealWeight.apply_ne_zero_iff_isGood and
TauCeti.UnitaryIdealWeight.norm_eq_one.
Main declarations #
TauCeti.MultiplicativeIdealWeight: the general completely multiplicative carrier, itsTauCeti.MultiplicativeIdealWeight.badPrimesand its good ideals (TauCeti.MultiplicativeIdealWeight.IsGood);TauCeti.MultiplicativeIdealWeight.apply_ne_zero_iff_isGood: a weight is nonzero exactly on the good ideals;TauCeti.MultiplicativeIdealWeight.ext_heightOneSpectrum: a weight is determined by its values at the height-one primes;TauCeti.MultiplicativeIdealWeight.ofBadPrimes, the pointwiseCommMonoidstructure (whose unit is the trivial weight),TauCeti.MultiplicativeIdealWeight.restrict,TauCeti.MultiplicativeIdealWeight.conjandTauCeti.MultiplicativeIdealWeight.normTwist: the constructors and operations;TauCeti.MultiplicativeIdealWeight.badPrimes_pow,TauCeti.MultiplicativeIdealWeight.conj_pow,TauCeti.MultiplicativeIdealWeight.normTwist_powandTauCeti.MultiplicativeIdealWeight.restrict_pow, with their unitary counterparts: powers, in particular the pointwise squareΟ ^ 2used by the3-4-1argument, keep the bad primes and commute with the operations, then-th power of a twist byzbeing the twist byn * z. Preservation of bad primes and compatibility with restriction require a nonzero exponent;TauCeti.MultiplicativeIdealWeight.IsNormTwistOnGoodandTauCeti.MultiplicativeIdealWeight.IsTrivialOnGood: the weights agreeing with a purely imaginary norm twist, respectively with the trivial weight, on their good ideals, with the structure theoremTauCeti.MultiplicativeIdealWeight.IsNormTwistOnGood.eq_normTwist, its converseTauCeti.MultiplicativeIdealWeight.isNormTwistOnGood_normTwist_ofBadPrimes, and the behaviour of the parameter under conjugation, the pointwise product, powers and a further twist;TauCeti.MultiplicativeIdealWeight.toIdealArithmeticFunction: passage to the general carrier, inverted byTauCeti.IdealArithmeticFunction.zeroExtend;TauCeti.UnitaryIdealWeight: the unitary subtype, withTauCeti.UnitaryIdealWeight.norm_eq_oneon all good ideals,TauCeti.UnitaryIdealWeight.norm_normTwistfor the modulus of an arbitrary norm twist,TauCeti.UnitaryIdealWeight.ofPowEqOnefor finite-order weights, and the operationsTauCeti.UnitaryIdealWeight.conj,TauCeti.UnitaryIdealWeight.restrictandTauCeti.UnitaryIdealWeight.normTwist(the last for the imaginary norm twists only), andTauCeti.UnitaryIdealWeight.toIdealArithmeticFunctionfor its passage to the general carrier;TauCeti.MultiplicativeIdealWeight.mapandTauCeti.UnitaryIdealWeight.map, with their multiplicative equivalencesmapEquiv: functoriality under an isomorphismK β+* Lof the ambient fields, together with the identity and composition laws, the preservation of the pointwise product (map_oneandmap_mulon both carriers), the naturality of restriction, conjugation and norm twists, and the compatibilitiesTauCeti.MultiplicativeIdealWeight.badPrimes_mapandTauCeti.MultiplicativeIdealWeight.toIdealArithmeticFunction_map.
Negative results #
Two negative results delimit the carriers.
TauCeti.MultiplicativeIdealWeight.coe_ne_const_one says the everywhere-one function on all
integral ideals underlies no weight, because β*β forces the value 0 at β₯ β the
everywhere-one function on the nonzero ideals is the trivial weight instead
(TauCeti.MultiplicativeIdealWeight.toIdealArithmeticFunction_one).
TauCeti.UnitaryIdealWeight.norm_normTwist_apply_ne_one says that a norm twist with
Re z β 0 has modulus different from one at every ideal of absolute norm greater than one, so
such twists live only in the general carrier.
References #
- J. Neukirch, Algebraic Number Theory, Chapter VII.
The general carrier of completely multiplicative ideal weights #
A multiplicative ideal weight on a number field K: a completely multiplicative
complex-valued function on all integral ideals of π K, packaged as a monoid-with-zero
homomorphism Ideal (π K) β*β β, which kills only finitely many height-one primes.
Being a β*β forces the value 0 at the zero ideal β₯ and the value 1 at β€; the
finiteness condition is what makes the associated Euler product have finitely many bad local
factors. This carrier is degree one: its value at a prime power π ^ n is forced to be
Ο π ^ n, so it excludes the ideal MΓΆbius function and any coefficient system whose
prime-power values are independent local data.
The underlying completely multiplicative map on all integral ideals.
- finite_setOf_apply_eq_zero : {π : IsDedekindDomain.HeightOneSpectrum (NumberField.RingOfIntegers K) | self.toMonoidWithZeroHom π.asIdeal = 0}.Finite
Only finitely many height-one primes are killed.
Instances For
Equations
- TauCeti.MultiplicativeIdealWeight.instFunLikeIdealRingOfIntegersComplex = { coe := fun (Ο : TauCeti.MultiplicativeIdealWeight K) => βΟ.toMonoidWithZeroHom, coe_injective := β― }
The zero-ideal law. Every multiplicative ideal weight kills the zero ideal, so no weight is the everywhere-one function on all ideals.
A multiplicative ideal weight is determined by its values at the height-one primes: every
nonzero ideal of π K is a product of them.
The bad primes of an ideal weight: the height-one primes it kills. This is a derived, canonically determined accessor, not extra data.
Equations
- Ο.badPrimes = {π : IsDedekindDomain.HeightOneSpectrum (NumberField.RingOfIntegers K) | Ο π.asIdeal = 0}
Instances For
An ideal is good for Ο when it is prime to the bad primes of Ο. In particular a
good ideal is nonzero, even when Ο has no bad primes at all.
Instances For
A completely multiplicative ideal weight is nonzero exactly on the good ideals. Thus the good ideals are precisely the nonvanishing locus of the weight.
Constructors and operations #
The indicator weight of a finite set S of height-one primes: the value is 1 on the
ideals prime to S and 0 elsewhere. Its bad primes are exactly S, and ofBadPrimes β
is
the trivial weight 1.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Defining equation of TauCeti.MultiplicativeIdealWeight.ofBadPrimes; its body is not
exposed.
The pointwise product of two multiplicative ideal weights.
Equations
- One or more equations did not get rendered due to their size.
The trivial multiplicative ideal weight.
The trivial weight is the indicator of the nonzero ideals.
The pointwise product of multiplicative ideal weights, with the trivial weight as unit. It is
not the Dirichlet convolution of ideal arithmetic functions, which is
TauCeti.IdealArithmeticFunction.convolution.
Equations
- One or more equations did not get rendered due to their size.
A positive power of a weight is computed pointwise. The exponent must be nonzero: Ο ^ 0 is
the trivial weight, which vanishes at β₯, while Ο β₯ ^ 0 = 1.
A nonzero power of a weight kills exactly the primes the weight kills, so it has the same good ideals.
Restriction away from a finite set of primes: Ο is left unchanged on the ideals prime
to S and set to 0 on the others.
Equations
- Ο.restrict S hS = Ο * TauCeti.MultiplicativeIdealWeight.ofBadPrimes S hS
Instances For
Restricting away from no prime at all changes nothing.
Forbidding one more prime. Restricting away from insert π S kills the ideals divisible
by π and agrees with the restriction away from S on the others.
Restricting the trivial weight away from S gives the indicator weight of ideals prime to
every prime in S.
Restriction commutes with nonzero powers. The exponent must be nonzero:
(Ο ^ 0).restrict S hS is the indicator weight ofBadPrimes S hS, while
Ο.restrict S hS ^ 0 is the trivial weight.
The conjugate weight I β¦ conj (Ο I).
Equations
- Ο.conj = { toMonoidWithZeroHom := (β(starRingEnd β)).comp Ο.toMonoidWithZeroHom, finite_setOf_apply_eq_zero := β― }
Instances For
Conjugation is multiplicative for the pointwise product.
Conjugation commutes with powers; in particular the conjugate of the pointwise square is the square of the conjugate.
The norm twist I β¦ Ο I * N(I) ^ (-z). For general z this leaves the unitary
carrier; only the purely imaginary twists preserve it
(TauCeti.UnitaryIdealWeight.normTwist).
Equations
- One or more equations did not get rendered due to their size.
Instances For
Successive norm twists combine by adding their parameters.
The pointwise product of two norm twists is the twist of the product by the sum of the parameters.
The n-th power of a norm twist is the twist of the n-th power by n times the
parameter. For n = 2: the pointwise square of the twist of Ο by N(I) ^ (-z) is the twist of
Ο ^ 2 by N(I) ^ (-2z).
Weights that are norm twists on their good locus #
A weight is a norm twist on its good ideals, with parameter u, when
Ο I = N(I) ^ (u * I) at every ideal I prime to its bad primes. Away from the bad primes such
a weight is the purely imaginary norm twist TauCeti.MultiplicativeIdealWeight.normTwist of the
trivial weight, and it is the whole of that twist once the bad primes are taken into account
(TauCeti.MultiplicativeIdealWeight.IsNormTwistOnGood.eq_normTwist).
These weights give degenerate examples in families of ideal weights: their L-series is a
Dedekind zeta function with finitely many Euler factors deleted, read after an imaginary
translation, so it has a pole and no cancellation in its ideal partial sums
(TauCeti.not_hasCancellation_of_isNormTwistOnGood).
Equations
- Ο.IsNormTwistOnGood u = β (I : Ideal (NumberField.RingOfIntegers K)), Ο.IsGood I β Ο I = β(Ideal.absNorm I) ^ (βu * Complex.I)
Instances For
A weight is trivial on its good ideals when it takes the value 1 at every ideal prime
to its bad primes; equivalently it is a norm twist on its good ideals with parameter 0
(TauCeti.MultiplicativeIdealWeight.isNormTwistOnGood_zero_iff).
Equations
- Ο.IsTrivialOnGood = β (I : Ideal (NumberField.RingOfIntegers K)), Ο.IsGood I β Ο I = 1
Instances For
A weight trivial on its good ideals takes the value 1 at each of them.
The norm twists with parameter 0 on the good ideals are the weights that are trivial
there.
The trivial weight is trivial on its good ideals, which are all the nonzero ideals.
The indicator of the ideals prime to a finite set S of primes is trivial on its good
ideals, which are exactly those ideals.
A norm twist on the good ideals is a norm twist of an indicator weight. A weight that is
a norm twist with parameter u on its good ideals is the twist by N(I) ^ (u * I) of the
indicator of the ideals prime to its bad primes. The bad set is a parameter, so that a caller
holding it as a Finset need not convert.
A twist adds to the parameter. Twisting by N(I) ^ (v * I) turns a norm twist with
parameter u on the good ideals into one with parameter u + v; the good ideals are unchanged.
Converse of TauCeti.MultiplicativeIdealWeight.IsNormTwistOnGood.eq_normTwist. The
twist by N(I) ^ (u * I) of the indicator of the ideals prime to a finite set of primes is a
norm twist with parameter u on its good ideals.
Conjugation negates the parameter of a norm twist on the good ideals.
The pointwise product adds the parameters of two norm twists on the good ideals. Both factors are good at every ideal good for the product, since the bad primes of a product are the union of those of its factors.
The n-th power multiplies the parameter by n for a norm twist on the good ideals. For
n = 2 this identifies the pointwise square of such a weight as a norm twist with parameter 2u
on its good ideals.
Passage to the general carrier, and the zero-ideal rejection test #
The ideal arithmetic function underlying an ideal weight: its restriction to the nonzero ideals.
Equations
Instances For
The ideal arithmetic function underlying a norm twist multiplies by N(I) ^ (-z).
Regrouping absorbs a norm twist. Twisting a weight by N(I) ^ (-z) twists its n-th norm
coefficient by n ^ (-z).
The ideal arithmetic function underlying a completely multiplicative ideal weight is multiplicative on relatively prime ideals.
An ideal weight is recovered from its restriction to the nonzero ideals by extending by
zero: the zero-ideal law Ο β₯ = 0 is exactly what makes this work.
Rejection test. The everywhere-one function on all integral ideals underlies no
multiplicative ideal weight, since Ideal (π K) β*β β forces the value 0 at β₯. The
everywhere-one function on the nonzero ideals is the trivial weight
(TauCeti.MultiplicativeIdealWeight.toIdealArithmeticFunction_one).
Functoriality under an isomorphism of fields #
Transport along an isomorphism of fields. An isomorphism e : K β+* L carries a
multiplicative ideal weight on K to one on L, by pulling ideals of π L back to π K
along NumberField.RingOfIntegers.mapRingEquiv e.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The bad primes transport too: they are carried along by the induced bijection of height-one spectra.
Transport is functorial: transporting along e and then along e' is the same as
transporting along e.trans e'.
Transport preserves the pointwise CommMonoid structure.
Transport along an isomorphism of fields, as a multiplicative equivalence of the two
carriers, with inverse the transport along e.symm.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Transport carries an indicator weight to the indicator of the image prime set.
Transport commutes with restriction after carrying the excluded prime set forward.
Transport commutes with complex conjugation.
Transport commutes with norm twists because absolute ideal norm is invariant under a ring equivalence.
The unitary subtype #
A unitary ideal weight: a multiplicative ideal weight whose values have modulus 1
away from its bad primes. Finite-order Hecke characters land here
(TauCeti.UnitaryIdealWeight.ofPowEqOne), and so do the purely imaginary norm twists
(TauCeti.UnitaryIdealWeight.normTwist); a norm twist with Re z β 0 does not
(TauCeti.UnitaryIdealWeight.norm_normTwist_apply_ne_one).
Equations
Instances For
A unitary weight has modulus one on every good ideal, extending its defining condition from good primes to the entire good-ideal locus.
A unitary weight is bounded by one on every ideal. The bound is unconditional: it carries
no goodness hypothesis, so a comparison indexed by all of (Ideal (π K))β° can apply it termwise.
norm_eq_one is sharper where it applies, but obliges the caller to split that index type first;
this is the form a convergence estimate wants.
A weight trivial on its good ideals is unitary, so it is bounded by one on every ideal
(TauCeti.UnitaryIdealWeight.norm_le_one).
The trivial weight is unitary.
The pointwise product of unitary weights is unitary.
Equations
- TauCeti.UnitaryIdealWeight.instMul = { mul := fun (Ο Ο : TauCeti.UnitaryIdealWeight K) => β¨βΟ * βΟ, β―β© }
Pointwise multiplication makes the unitary weights a commutative monoid.
Equations
- One or more equations did not get rendered due to their size.
Finite-order weights are unitary. If a positive power of Ο takes the value 1 at
every good prime β as for a finite-order Hecke character β then Ο is unitary.
Equations
- TauCeti.UnitaryIdealWeight.ofPowEqOne Ο hn h = β¨Ο, β―β©
Instances For
Imaginary norm twists preserve unitarity. For Re z = 0 the factor N(I) ^ (-z) has
modulus 1, so the twisted weight is again unitary.
Equations
- TauCeti.UnitaryIdealWeight.normTwist z hz Ο = β¨TauCeti.MultiplicativeIdealWeight.normTwist z βΟ, β―β©
Instances For
The zero norm twist acts trivially on unitary weights.
Successive imaginary norm twists of a unitary weight combine by adding their parameters.
The pointwise product of two imaginary norm twists of unitary weights is the twist of the product by the sum of the parameters.
The n-th power of an imaginary norm twist of a unitary weight is the twist of the
n-th power by n times the parameter.
The modulus of an arbitrary norm twist. At a good ideal, twisting a unitary weight by
z gives modulus N(I) ^ (-Re z); only the purely imaginary twists therefore stay unitary.
Rejection test. A norm twist with Re z β 0 leaves the unitary carrier: at every ideal
of absolute norm greater than one its modulus differs from 1, being N(I) ^ (-Re z) at a good
ideal and 0 elsewhere. Such twists therefore live only in TauCeti.MultiplicativeIdealWeight.
The conjugate of a unitary weight is unitary.
Instances For
Conjugation of unitary weights is multiplicative for the pointwise product.
Conjugation of unitary weights commutes with powers, in particular with the pointwise square.
Restricting a unitary weight away from a finite set of primes keeps it unitary: the restricted weight is unchanged at the primes that are good for it.
Instances For
Restricting a unitary weight away from no prime at all changes nothing.
Restriction of unitary weights commutes with nonzero powers, in particular with the
pointwise square. As for TauCeti.MultiplicativeIdealWeight.restrict_pow, the exponent 0 is
excluded.
Transport along an isomorphism of fields preserves unitarity: the transported weight has
the same values as Ο, read off at the corresponding primes.
Equations
- TauCeti.UnitaryIdealWeight.map e Ο = β¨TauCeti.MultiplicativeIdealWeight.map e βΟ, β―β©
Instances For
Transport is functorial on the unitary carrier as well.
Transport preserves the pointwise CommMonoid structure of the unitary carrier too.
Transport along an isomorphism of fields, as a multiplicative equivalence of the unitary carriers.
Equations
- TauCeti.UnitaryIdealWeight.mapEquiv e = { toFun := TauCeti.UnitaryIdealWeight.map e, invFun := TauCeti.UnitaryIdealWeight.map e.symm, left_inv := β―, right_inv := β―, map_mul' := β― }
Instances For
Transport commutes with restriction on unitary weights after carrying the excluded prime set forward.
Transport commutes with complex conjugation on unitary weights.
Transport commutes with purely imaginary norm twists on unitary weights.
The ideal arithmetic function underlying a unitary weight: the restriction of the underlying multiplicative weight to the nonzero ideals.
Equations
- Ο.toIdealArithmeticFunction = (βΟ).toIdealArithmeticFunction
Instances For
The ideal arithmetic function of a unitary weight agrees with that of its underlying multiplicative weight.
Regrouping absorbs an imaginary norm twist. For z.re = 0, twisting a unitary weight by
N(I) ^ (-z) multiplies its n-th norm coefficient by n ^ (-z).
The ideal arithmetic function underlying a unitary ideal weight is multiplicative on relatively prime ideals.
A unitary weight is recovered from its underlying ideal arithmetic function by extending
by zero, just as in TauCeti.MultiplicativeIdealWeight.zeroExtend_toIdealArithmeticFunction.
The trivial unitary weight restricts to the constant-one ideal arithmetic function.
A unitary weight is determined by its ideal arithmetic function.