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feat: finite dimensional distribution of Brownian motion#36472

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EtienneC30:gauss_proj
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feat: finite dimensional distribution of Brownian motion#36472
EtienneC30 wants to merge 42 commits intoleanprover-community:masterfrom
EtienneC30:gauss_proj

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@EtienneC30 EtienneC30 commented Mar 11, 2026

Define gaussianProjectiveFamily : (I : Finset ℝ≥0) → Measure (I → ℝ). Each gaussianProjectiveFamily I is the centered Gaussian measure over I → ℝ with covariance matrix given by brownianCovMatrix I s t := min s t.

Prove that these measures satisfy IsProjectiveMeasureFamily, which means that they can be extended into a measure over ℝ≥0 → ℝ thanks to the Kolmogorov's extension theorem (not in Mathlib yet). The obtained measure is a measure over the set of real processes indexed by ℝ≥0 and is the law of the Brownian motion.


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@EtienneC30 EtienneC30 added blocked-by-other-PR This PR depends on another PR (this label is automatically managed by a bot) t-measure-probability Measure theory / Probability theory brownian Part of the ongoing formalization of the Brownian motion and stochastic integrals labels Mar 11, 2026
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PR summary 595196b114

Import changes for modified files

Dependency changes

File Base Count Head Count Change
Mathlib.MeasureTheory.Function.L2Space 2372 2383 +11 (+0.46%)
Mathlib.Probability.Moments.Basic 2455 2466 +11 (+0.45%)
Mathlib.Probability.Distributions.Gaussian.HasGaussianLaw.Basic 2731 2742 +11 (+0.40%)
Import changes for all files
Files Import difference
5 files Mathlib.Probability.Distributions.Gaussian.CharFun Mathlib.Probability.Distributions.Gaussian.HasGaussianLaw.Independence Mathlib.Probability.Distributions.Gaussian.IsGaussianProcess.Independence Mathlib.Probability.Distributions.Gaussian.Multivariate Mathlib.Probability.Moments.CovarianceBilin
1
12 files Mathlib.NumberTheory.LSeries.DirichletContinuation Mathlib.NumberTheory.LSeries.Nonvanishing Mathlib.NumberTheory.LSeries.PrimesInAP Mathlib.NumberTheory.LSeries.ZMod Mathlib.NumberTheory.MahlerMeasure Mathlib.NumberTheory.ModularForms.DedekindEta Mathlib.NumberTheory.ModularForms.Delta Mathlib.NumberTheory.ModularForms.EisensteinSeries.E2.MDifferentiable Mathlib.NumberTheory.ModularForms.EisensteinSeries.E2.Summable Mathlib.NumberTheory.ModularForms.EisensteinSeries.E2.Transform Mathlib.NumberTheory.ModularForms.EisensteinSeries.QExpansion Mathlib.NumberTheory.ModularForms.JacobiTheta.Manifold
9
98 files Mathlib.Analysis.Distribution.FourierMultiplier Mathlib.Analysis.Distribution.SchwartzSpace.Basic Mathlib.Analysis.Distribution.SchwartzSpace.Deriv Mathlib.Analysis.Distribution.SchwartzSpace.Fourier Mathlib.Analysis.Distribution.SchwartzSpace Mathlib.Analysis.Distribution.TemperedDistribution Mathlib.Analysis.Fourier.AddCircleMulti Mathlib.Analysis.Fourier.AddCircle Mathlib.Analysis.Fourier.Convolution Mathlib.Analysis.Fourier.FourierTransformDeriv Mathlib.Analysis.Fourier.LpSpace Mathlib.Analysis.Fourier.PoissonSummation Mathlib.Analysis.Polynomial.Fourier Mathlib.Analysis.Polynomial.MahlerMeasure Mathlib.Analysis.SpecialFunctions.Gaussian.PoissonSummation Mathlib.MeasureTheory.Function.ConditionalExpectation.Basic Mathlib.MeasureTheory.Function.ConditionalExpectation.CondexpL1 Mathlib.MeasureTheory.Function.ConditionalExpectation.CondexpL2 Mathlib.MeasureTheory.Function.ConditionalExpectation.Indicator Mathlib.MeasureTheory.Function.ConditionalExpectation.LebesgueBochner Mathlib.MeasureTheory.Function.ConditionalExpectation.PullOut Mathlib.MeasureTheory.Function.ConditionalExpectation.RadonNikodym Mathlib.MeasureTheory.Function.ConditionalExpectation.Real Mathlib.MeasureTheory.Function.ConditionalLExpectation Mathlib.MeasureTheory.Function.FactorsThrough Mathlib.MeasureTheory.Function.L2Space Mathlib.MeasureTheory.Measure.CharacteristicFunction.TaylorExpansion Mathlib.MeasureTheory.Measure.LevyConvergence Mathlib.NumberTheory.EulerProduct.DirichletLSeries Mathlib.NumberTheory.Harmonic.ZetaAsymp Mathlib.NumberTheory.LSeries.Dirichlet Mathlib.NumberTheory.LSeries.HurwitzZetaEven Mathlib.NumberTheory.LSeries.HurwitzZetaOdd Mathlib.NumberTheory.LSeries.HurwitzZetaValues Mathlib.NumberTheory.LSeries.HurwitzZeta Mathlib.NumberTheory.LSeries.RiemannZeta Mathlib.NumberTheory.ModularForms.EisensteinSeries.E2.Defs Mathlib.NumberTheory.ModularForms.JacobiTheta.Bounds Mathlib.NumberTheory.ModularForms.JacobiTheta.OneVariable Mathlib.NumberTheory.ModularForms.JacobiTheta.TwoVariable Mathlib.NumberTheory.ZetaValues Mathlib.Probability.BorelCantelli Mathlib.Probability.Combinatorics.BinomialRandomGraph.Defs Mathlib.Probability.CondVar Mathlib.Probability.ConditionalExpectation Mathlib.Probability.Distributions.Gaussian.Basic Mathlib.Probability.Distributions.Gaussian.Fernique Mathlib.Probability.Distributions.Gaussian.HasGaussianLaw.Basic Mathlib.Probability.Distributions.Gaussian.HasGaussianLaw.Def Mathlib.Probability.Distributions.Gaussian.IsGaussianProcess.Basic Mathlib.Probability.Distributions.Gaussian.IsGaussianProcess.Def Mathlib.Probability.Distributions.Gaussian.Real Mathlib.Probability.Distributions.SetBernoulli Mathlib.Probability.HasLawExists Mathlib.Probability.HasLaw Mathlib.Probability.IdentDistribIndep Mathlib.Probability.IdentDistrib Mathlib.Probability.Independence.BoundedContinuousFunction Mathlib.Probability.Independence.Conditional Mathlib.Probability.Independence.InfinitePi Mathlib.Probability.Independence.Integration Mathlib.Probability.Independence.ZeroOne Mathlib.Probability.Kernel.CompProdEqIff Mathlib.Probability.Kernel.Composition.AbsolutelyContinuous Mathlib.Probability.Kernel.CondDistrib Mathlib.Probability.Kernel.Condexp Mathlib.Probability.Kernel.Disintegration.Density Mathlib.Probability.Kernel.Disintegration.Integral Mathlib.Probability.Kernel.Disintegration.StandardBorel Mathlib.Probability.Kernel.Disintegration.Unique Mathlib.Probability.Kernel.IonescuTulcea.Traj Mathlib.Probability.Kernel.Posterior Mathlib.Probability.Kernel.RadonNikodym Mathlib.Probability.Martingale.Basic Mathlib.Probability.Martingale.BorelCantelli Mathlib.Probability.Martingale.Centering Mathlib.Probability.Martingale.Convergence Mathlib.Probability.Martingale.OptionalSampling Mathlib.Probability.Martingale.OptionalStopping Mathlib.Probability.Martingale.Upcrossing Mathlib.Probability.Moments.Basic Mathlib.Probability.Moments.ComplexMGF Mathlib.Probability.Moments.CovarianceBilinDual Mathlib.Probability.Moments.Covariance Mathlib.Probability.Moments.MGFAnalytic Mathlib.Probability.Moments.SubGaussian Mathlib.Probability.Moments.Tilted Mathlib.Probability.Moments.Variance Mathlib.Probability.Notation Mathlib.Probability.Process.Adapted Mathlib.Probability.Process.Filtration Mathlib.Probability.Process.FiniteDimensionalLaws Mathlib.Probability.Process.HittingTime Mathlib.Probability.Process.PartitionFiltration Mathlib.Probability.Process.Predictable Mathlib.Probability.Process.Stopping Mathlib.Probability.ProductMeasure Mathlib.Probability.StrongLaw
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Mathlib.Probability.BrownianMotion.GaussianProjectiveFamily (new file) 2848

Declarations diff

+ HasGaussianLaw.map_eq_gaussianReal
+ _root_.MeasureTheory.posSemidef_matrix_measure_inter
+ brownianCovMatrix
+ brownianCovMatrix_apply
+ brownianCovMatrix_submatrix
+ covariance_eval_gaussianProjectiveFamily
+ covariance_gaussianProjectiveFamily
+ gaussianProjectiveFamily
+ integral_comp_id_comm
+ integral_comp_id_comm'
+ integral_eval_gaussianProjectiveFamily
+ integral_gaussianProjectiveFamily
+ integral_id_gaussianProjectiveFamily
+ integral_id_gaussianProjectiveFamily'
+ integral_id_map
+ isGaussian_gaussianProjectiveFamily
+ isProjectiveMeasureFamily_gaussianProjectiveFamily
+ measurePreserving_eval_gaussianProjectiveFamily
+ measurePreserving_eval_sub_eval_gaussianProjectiveFamily
+ measurePreserving_ofLp_multivariateGaussian
+ measurePreserving_restrict_gaussianProjectiveFamily
+ measurePreserving_toLp_gaussianProjectiveFamily
+ posSemidef_brownianCovMatrix
+ variance_eval_gaussianProjectiveFamily
+ variance_gaussianProjectiveFamily

You can run this locally as follows
## summary with just the declaration names:
./scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.


Increase in tech debt: (relative, absolute) = (2.00, 0.00)
Current number Change Type
9490 2 backward.isDefEq

Current commit 99180b3cc5
Reference commit 595196b114

You can run this locally as

./scripts/reporting/technical-debt-metrics.sh pr_summary
  • The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
  • The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

@EtienneC30 EtienneC30 removed the blocked-by-other-PR This PR depends on another PR (this label is automatically managed by a bot) label Mar 16, 2026
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