Bessel potential spaces #
We define the Bessel potential space or Fourier-theoretic Sobolev space, with smoothness parameter
s and integrability parameter p. Informally, this space is given as the set of all tempered
distributions u such that 𝓕⁻ (1 + ‖ξ‖ ^ 2) ^ (s / 2) 𝓕 u is an Lp function.
Implementation notes #
In Mathlib.Analysis.Distribution.Sobolev the unbundled version TemperedDistribution.MemSobolev
is defined as ∃ v : Lp, besselPotential E F s u = v. While it would be possible to define
the bundled space in the same way, the existence quantifier makes proving theorems more involved and
hence we bundle the Lp function v into the structure.
We also note that since every Lp function uniquely defines a distribution via
u = besselPotential E F (-s) v, it would be possible to define the Bessel potential space
as a one-field structure of Lp. The approach of having both u and v as part of the structure
gives better definitional equalities.
The Bessel potential space of order s : ℝ and p : ℝ≥0∞, also known as the Sobolev space and
usually denoted by H^{s,p}.
It is defined as the set of all tempered distributions u such that
𝓕⁻ (1 + ‖x‖ ^ 2) ^ (s / 2) 𝓕 u can be represented by a Lp function v. Both u and v are
stored as data to avoid using Classical.choose.
- toDistr : TemperedDistribution E F
The underlying tempered distribution
- toLp : ↥(MeasureTheory.Lp F p MeasureTheory.volume)
The underlying
Lpfunction - bessel_toDistr_eq_toLp : (TemperedDistribution.besselPotential E F s) ↑self = MeasureTheory.Lp.toTemperedDistribution self.toLp
The
Lpfunction is obtained by applying the Bessel potential operator to the distribution
Instances For
The Bessel potential space of order s : ℝ and p : ℝ≥0∞, also known as the Sobolev space and
usually denoted by H^{s,p}.
It is defined as the set of all tempered distributions u such that
𝓕⁻ (1 + ‖x‖ ^ 2) ^ (s / 2) 𝓕 u can be represented by a Lp function v. Both u and v are
stored as data to avoid using Classical.choose.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The Bessel potential space of order s : ℝ and p : ℝ≥0∞, also known as the Sobolev space and
usually denoted by H^{s,p}.
It is defined as the set of all tempered distributions u such that
𝓕⁻ (1 + ‖x‖ ^ 2) ^ (s / 2) 𝓕 u can be represented by a Lp function v. Both u and v are
stored as data to avoid using Classical.choose.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The Bessel potential space of order s : ℝ and p : ℝ≥0∞, also known as the Sobolev space and
usually denoted by H^{s,p}.
It is defined as the set of all tempered distributions u such that
𝓕⁻ (1 + ‖x‖ ^ 2) ^ (s / 2) 𝓕 u can be represented by a Lp function v. Both u and v are
stored as data to avoid using Classical.choose.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The Bessel potential space of order s : ℝ and p : ℝ≥0∞, also known as the Sobolev space and
usually denoted by H^{s,p}.
It is defined as the set of all tempered distributions u such that
𝓕⁻ (1 + ‖x‖ ^ 2) ^ (s / 2) 𝓕 u can be represented by a Lp function v. Both u and v are
stored as data to avoid using Classical.choose.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Equations
- BesselPotentialSpace.instCoeHeadTemperedDistribution = { coe := fun (f : BesselPotentialSpace E F s p) => ↑f }
Transfer a Sobolev function in H^{s,p} to H^{s', p} given that s = s'.
Equations
- BesselPotentialSpace.copy s' f hs = { toDistr := ↑f, toLp := f.toLp, bessel_toDistr_eq_toLp := ⋯ }
Instances For
Equations
- BesselPotentialSpace.instNeg = { neg := fun (f : BesselPotentialSpace E F s p) => { toDistr := -↑f, toLp := -f.toLp, bessel_toDistr_eq_toLp := ⋯ } }
Equations
- BesselPotentialSpace.instSMul = { smul := fun (c : R) (f : BesselPotentialSpace E F s p) => { toDistr := c • ↑f, toLp := c • f.toLp, bessel_toDistr_eq_toLp := ⋯ } }
Equations
- One or more equations did not get rendered due to their size.
Coercion to tempered distributions as an additive homomorphism.
Equations
- BesselPotentialSpace.coeAddMonoidHom E F s p = { toFun := fun (f : BesselPotentialSpace E F s p) => ↑f, map_zero' := ⋯, map_add' := ⋯ }
Instances For
Equations
- BesselPotentialSpace.instModuleComplex = { toSMul := BesselPotentialSpace.instSMul, mul_smul := ⋯, one_smul := ⋯, smul_zero := ⋯, smul_add := ⋯, add_smul := ⋯, zero_smul := ⋯ }
The map u ↦ 𝓕⁻ (1 + ‖x‖ ^ 2) ^ (s / 2) 𝓕 u as a linear map from H^{s,p} to Lp.
See toLpₗᵢ for the linear isometry equivalence.
Equations
- BesselPotentialSpace.toLpₗ E F s p = { toFun := BesselPotentialSpace.toLp, map_add' := ⋯, map_smul' := ⋯ }
Instances For
Every Lp function defines a Sobolev function by f ↦ besselPotential E F (-s) f.
Equations
- BesselPotentialSpace.ofLp s f = { toDistr := (TemperedDistribution.besselPotential E F (-s)) (MeasureTheory.Lp.toTemperedDistribution f), toLp := f, bessel_toDistr_eq_toLp := ⋯ }
Instances For
Equations
- One or more equations did not get rendered due to their size.
Equations
- BesselPotentialSpace.instNormedSpaceComplex = { toModule := BesselPotentialSpace.instModuleComplex, norm_smul_le := ⋯ }
The linear isometry between H^{s,p} and Lp.
Equations
- BesselPotentialSpace.toLpₗᵢ E F s p = { toLinearMap := BesselPotentialSpace.toLpₗ E F s p, invFun := BesselPotentialSpace.ofLp s, left_inv := ⋯, right_inv := ⋯, norm_map' := ⋯ }
Instances For
Equations
- One or more equations did not get rendered due to their size.
Every unbundled Sobolev tempered distribution defines an element in H^{s, p}.
Equations
- hf.toBesselPotentialSpace = { toDistr := f, toLp := Exists.choose hf, bessel_toDistr_eq_toLp := ⋯ }