ℓp space #
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This file describes properties of elements f of a pi-type Π i, E i with finite "norm",
defined for p:ℝ≥0∞ as the size of the support of f if p=0, (∑' a, ‖f a‖^p) ^ (1/p) for
0 < p < ∞ and ⨆ a, ‖f a‖ for p=∞.
The Prop-valued mem_ℓp f p states that a function f : Π i, E i has finite norm according
to the above definition; that is, f has finite support if p = 0, summable (λ a, ‖f a‖^p) if
0 < p < ∞, and bdd_above (norm '' (set.range f)) if p = ∞.
The space lp E p is the subtype of elements of Π i : α, E i which satisfy mem_ℓp f p. For
1 ≤ p, the "norm" is genuinely a norm and lp is a complete metric space.
Main definitions #
mem_ℓp f p: property that the functionfsatisfies, as appropriate,ffinitely supported ifp = 0,summable (λ a, ‖f a‖^p)if0 < p < ∞, andbdd_above (norm '' (set.range f))ifp = ∞.lp E p: elements ofΠ i : α, E isuch thatmem_ℓp f p. Defined as anadd_subgroupof a type synonympre_lpforΠ i : α, E i, and equipped with anormed_add_comm_groupstructure. Under appropriate conditions, this is also equipped with the instanceslp.normed_space,lp.complete_space. Forp=∞, there is alsolp.infty_normed_ring,lp.infty_normed_algebra,lp.infty_star_ringandlp.infty_cstar_ring.
Main results #
mem_ℓp.of_exponent_ge: Forq ≤ p, a function which ismem_ℓpforqis alsomem_ℓpforplp.mem_ℓp_of_tendsto,lp.norm_le_of_tendsto: A pointwise limit of functions inlp, all withlpnorm≤ C, is itself inlpand haslpnorm≤ C.lp.tsum_mul_le_mul_norm: basic form of Hölder's inequality
Implementation #
Since lp is defined as an add_subgroup, dot notation does not work. Use lp.norm_neg f to
say that ‖-f‖ = ‖f‖, instead of the non-working f.norm_neg.
TODO #
- More versions of Hölder's inequality (for example: the case
p = 1,q = ∞; a version for normed rings which has‖∑' i, f i * g i‖rather than∑' i, ‖f i‖ * g i‖on the RHS; a version for three exponents satisfying1 / r = 1 / p + 1 / q)
The property that f : Π i : α, E i
- is finitely supported, if
p = 0, or - admits an upper bound for
set.range (λ i, ‖f i‖), ifp = ∞, or - has the series
∑' i, ‖f i‖ ^ pbe summable, if0 < p < ∞.
We define pre_lp E to be a type synonym for Π i, E i which, importantly, does not inherit
the pi topology on Π i, E i (otherwise this topology would descend to lp E p and conflict
with the normed group topology we will later equip it with.)
We choose to deal with this issue by making a type synonym for Π i, E i rather than for the lp
subgroup itself, because this allows all the spaces lp E p (for varying p) to be subgroups of
the same ambient group, which permits lemma statements like lp.monotone (below).
Equations
lp space
Equations
Instances for ↥lp
- lp.pi.has_coe
- lp.has_coe_to_fun
- lp.has_norm
- lp.normed_add_comm_group
- lp.module
- lp.smul_comm_class
- lp.is_scalar_tower
- lp.is_central_scalar
- lp.has_bounded_smul
- lp.normed_space
- lp.has_star
- lp.has_involutive_star
- lp.star_add_monoid
- lp.normed_star_group
- lp.star_module
- lp.has_mul
- lp.non_unital_ring
- lp.non_unital_normed_ring
- lp.infty_is_scalar_tower
- lp.infty_smul_comm_class
- lp.infty_star_ring
- lp.infty_cstar_ring
- lp.infty_ring
- lp.norm_one_class
- lp.infty_normed_ring
- lp.infty_comm_ring
- lp.infty_normed_comm_ring
- lp.infty_normed_algebra
- lp.complete_space
- lp.inner_product_space
Equations
Equations
- lp.normed_add_comm_group = {to_fun := has_norm.norm lp.has_norm, map_zero' := _, add_le' := _, neg' := _, eq_zero_of_map_eq_zero' := _}.to_normed_add_comm_group
Hölder inequality
Equations
- lp.pre_lp.module = pi.module α E 𝕜
The 𝕜-submodule of elements of Π i : α, E i whose lp norm is finite. This is lp E p,
with extra structure.
Equations
- lp.module = {to_distrib_mul_action := module.to_distrib_mul_action (lp_submodule E p 𝕜).module, add_smul := _, zero_smul := _}
Equations
- lp.normed_space = {to_module := lp.module lp.normed_space._proof_1, norm_smul_le := _}
Equations
- lp.has_star = {star := λ (f : ↥(lp E p)), ⟨has_star.star ⇑f, _⟩}
Equations
- lp.has_involutive_star = {to_has_star := lp.has_star lp.has_involutive_star._proof_1, star_involutive := _}
Equations
- lp.star_add_monoid = {to_has_involutive_star := lp.has_involutive_star lp.star_add_monoid._proof_1, star_add := _}
Equations
- lp.non_unital_ring = function.injective.non_unital_ring has_coe_to_fun.coe lp.non_unital_ring._proof_1 lp.non_unital_ring._proof_2 lp.non_unital_ring._proof_3 lp.non_unital_ring._proof_4 lp.non_unital_ring._proof_5 lp.non_unital_ring._proof_6 lp.non_unital_ring._proof_7 lp.non_unital_ring._proof_8
Equations
- lp.non_unital_normed_ring = {to_has_norm := normed_add_comm_group.to_has_norm lp.normed_add_comm_group, to_non_unital_ring := lp.non_unital_ring (λ (i : I), _inst_2 i), to_metric_space := normed_add_comm_group.to_metric_space lp.normed_add_comm_group, dist_eq := _, norm_mul := _}
Equations
- lp.infty_star_ring = {to_star_semigroup := {to_has_involutive_star := star_add_monoid.to_has_involutive_star (show star_add_monoid ↥(lp B ⊤), from let _inst : Π (i : I), star_add_monoid (B i) := λ (i : I), infer_instance in lp.star_add_monoid), star_mul := _}, star_add := _}
Equations
The 𝕜-subring of elements of Π i : α, B i whose lp norm is finite. This is lp E ∞,
with extra structure.
Equations
Equations
- lp.infty_normed_ring = {to_has_norm := non_unital_normed_ring.to_has_norm lp.non_unital_normed_ring, to_ring := {add := ring.add lp.infty_ring, add_assoc := _, zero := ring.zero lp.infty_ring, zero_add := _, add_zero := _, nsmul := ring.nsmul lp.infty_ring, nsmul_zero' := _, nsmul_succ' := _, neg := ring.neg lp.infty_ring, sub := ring.sub lp.infty_ring, sub_eq_add_neg := _, zsmul := ring.zsmul lp.infty_ring, zsmul_zero' := _, zsmul_succ' := _, zsmul_neg' := _, add_left_neg := _, add_comm := _, int_cast := ring.int_cast lp.infty_ring, nat_cast := ring.nat_cast lp.infty_ring, one := ring.one lp.infty_ring, nat_cast_zero := _, nat_cast_succ := _, int_cast_of_nat := _, int_cast_neg_succ_of_nat := _, mul := ring.mul lp.infty_ring, mul_assoc := _, one_mul := _, mul_one := _, npow := ring.npow lp.infty_ring, npow_zero' := _, npow_succ' := _, left_distrib := _, right_distrib := _}, to_metric_space := non_unital_normed_ring.to_metric_space lp.non_unital_normed_ring, dist_eq := _, norm_mul := _}
Equations
- lp.infty_comm_ring = {add := ring.add lp.infty_ring, add_assoc := _, zero := ring.zero lp.infty_ring, zero_add := _, add_zero := _, nsmul := ring.nsmul lp.infty_ring, nsmul_zero' := _, nsmul_succ' := _, neg := ring.neg lp.infty_ring, sub := ring.sub lp.infty_ring, sub_eq_add_neg := _, zsmul := ring.zsmul lp.infty_ring, zsmul_zero' := _, zsmul_succ' := _, zsmul_neg' := _, add_left_neg := _, add_comm := _, int_cast := ring.int_cast lp.infty_ring, nat_cast := ring.nat_cast lp.infty_ring, one := ring.one lp.infty_ring, nat_cast_zero := _, nat_cast_succ := _, int_cast_of_nat := _, int_cast_neg_succ_of_nat := _, mul := ring.mul lp.infty_ring, mul_assoc := _, one_mul := _, mul_one := _, npow := ring.npow lp.infty_ring, npow_zero' := _, npow_succ' := _, left_distrib := _, right_distrib := _, mul_comm := _}
Equations
A variant of pi.algebra that lean can't find otherwise.
Equations
Equations
The 𝕜-subalgebra of elements of Π i : α, B i whose lp norm is finite. This is lp E ∞,
with extra structure.
Equations
- lp.infty_normed_algebra = {to_algebra := {to_has_smul := algebra.to_has_smul (lp_infty_subalgebra 𝕜 B).algebra, to_ring_hom := algebra.to_ring_hom (lp_infty_subalgebra 𝕜 B).algebra, commutes' := _, smul_def' := _}, norm_smul_le := _}
The element of lp E p which is a : E i at the index i, and zero elsewhere.
The coercion from lp E p to Π i, E i is uniformly continuous.
"Semicontinuity of the lp norm": If all sufficiently large elements of a sequence in lp E p
have lp norm ≤ C, then the pointwise limit, if it exists, also has lp norm ≤ C.
If f is the pointwise limit of a bounded sequence in lp E p, then f is in lp E p.
If a sequence is Cauchy in the lp E p topology and pointwise convergent to a element f of
lp E p, then it converges to f in the lp E p topology.