diff --git a/LeanEval/Analysis/PDE/HyperbolicViscosity.lean b/LeanEval/Analysis/PDE/HyperbolicViscosity.lean new file mode 100644 index 000000000..ba0a9a6dd --- /dev/null +++ b/LeanEval/Analysis/PDE/HyperbolicViscosity.lean @@ -0,0 +1,68 @@ +import Mathlib.Analysis.InnerProductSpace.Laplacian +import Mathlib.FieldTheory.Separable +import Mathlib.LinearAlgebra.Charpoly.Basic +import Mathlib.Topology.EMetricSpace.BoundedVariation +import Mathlib.Topology.MetricSpace.Lipschitz +import EvalTools.Markers + +namespace LeanEval +namespace Analysis +namespace PDE + +/-! +# Total variation stability of viscous hyperbolic systems + +This file proves a stability estimate for solutions to the equation +$$u_t + A(u)u_x = u_xx$$, where $$A(u)$$ is an `n` by `n` strictly hyperbolic +matrix (i.e., it has `n` distinct real eigenvalues) which depends smoothly on $$u$$. + +The estimate, first proved in [1, Theorem 1], estimates the total variation of a solution at any time `t > 0` +in terms of the variation at the initial time (provided the initial variation is small). +Since the variation is invariant under spatial rescaling, the estimate is +uniform in the strength of the diffusion coefficient (which we take to be one for simplicity). +This allows to prove that vanishing viscosity approximations for hyperbolic conservation +laws converge to the entropy solutions. + +* [1]. Bianchini and Bressan, Vanishing viscosity solutions of nonlinear hyperbolic systems. Annals of Mathematics 161 (2005). +-/ +open Filter Topology Set Function +open scoped NNReal Nat EReal ContDiff + +local notation:arg "ℝ^" n:arg => EuclideanSpace ℝ (Fin n) + +variable (n : ℕ) (A : ℝ^n → (ℝ^n →L[ℝ] ℝ^n)) (K : Set ℝ^n) + +/-- `A` is (uniformly, smoothly) hyperbolic on `K` if `A` is smooth, +and for every `x ∈ K` it holds that `A x` has `n` real distinct eigenvalues. -/ +structure IsHyperbolicOn : Prop where + smooth : ContDiff ℝ ∞ A + real_ev x (hx : x ∈ K) : (A x).charpoly.Splits + distinct_ev x (hx : x ∈ K) : (A x).charpoly.Separable + +/-- `u` is a global smooth solution if `u` is continuous for all `t` and `x`, smooth for +`t > 0` and solves the PDE in the classical sense for `t > 0`. -/ +structure IsSmoothGlobalSolution (u : ℝ → ℝ → (ℝ^n)) : Prop where + diff : ContDiffOn ℝ ∞ (uncurry u) (Set.Ioi 0 ×ˢ Set.univ) + cont : ∀ t > 0, UniformContinuousOn (uncurry u) (Set.Icc 0 t ×ˢ Set.univ) + pde : ∀ t > 0, ∀ x, (deriv (u · x) t) + A (u t x) (deriv (u t ·) x) = iteratedDeriv 2 (u t ·) x + +/-- A total variation estimate holds if the total variation of any smooth solution +at time `t > 0` can be linearly estimated in terms of the total variation at time `0`, +provided the variation at time `0` is sufficiently small and the initial left limit of `u` +lies in `K` (see [1, Theorem 1]). +-/ +structure HasTVEstimateWith (δ C : EReal) : Prop where + estimate u (h_sol : IsSmoothGlobalSolution n A u) + (h_initial_tv : eVariationOn (u 0 ·) univ ≤ δ) + (h_initial_lim : ∃ x ∈ K, Tendsto (u 0 ·) atBot (𝓝 x)) + t (ht : t > 0) : eVariationOn (u t ·) univ ≤ C * eVariationOn (u 0 ·) univ + +/-- Total variation estimate for hyperbolic systems -/ +@[eval_problem] +theorem hyperbolic_viscosity (hn : 1 ≤ n) (hK : IsCompact K) (h : IsHyperbolicOn n A K) : + ∃ δ > 0, ∃ C < ⊤, HasTVEstimateWith n A K δ C := by + sorry + +end PDE +end Analysis +end LeanEval diff --git a/manifests/problems/hyperbolic_viscosity.toml b/manifests/problems/hyperbolic_viscosity.toml new file mode 100644 index 000000000..9d6c4c9fa --- /dev/null +++ b/manifests/problems/hyperbolic_viscosity.toml @@ -0,0 +1,13 @@ +id = "hyperbolic_viscosity" +title = "Total variation estimate for hyperbolic systems" +group = "formalization-evaluation" +status = "draft" +visible = true +statement_revision = 1 +tags = [] +test = false +module = "LeanEval.Analysis.PDE.HyperbolicViscosity" +holes = ["hyperbolic_viscosity"] +submitter = "Joris van Winden" +source = "Bianchini and Bressan, Vanishing viscosity solutions of nonlinear hyperbolic systems. Annals of Mathematics 161 (2005)." +informal_solution = "Bianchini and Bressan, Vanishing viscosity solutions of nonlinear hyperbolic systems. Annals of Mathematics 161 (2005)."