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Add InterlacingPR: Courant-Fischer monotonicity under Rayleigh-preserving embeddings (Cauchy interlacing core) - #50

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tukamilano merged 1 commit into
Lean-MoDS:mainfrom
everymonday100:add-interlacing-pr
Sep 11, 2026
Merged

tukamilano merged 1 commit into
Lean-MoDS:mainfrom
everymonday100:add-interlacing-pr

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@everymonday100

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Adds StatsMLlib/LinearAlgebra/Matrix/InterlacingPR.lean — reusable core of Cauchy eigenvalue interlacing for nested Hermitian principal blocks.

Contents

  • bddAbove_cfMaxMin_family / bddBelow_cfMinMax_family: boundedness of restricted Rayleigh families by operator norm
  • maxRayleighQuotientOn_map_eq: transport of restricted Rayleigh maximum along Rayleigh-preserving injective embeddings
  • cfMaxMin_mono_of_isometry / cfMinMax_mono_of_isometry: monotonicity of Courant-Fischer quantities (lower and upper halves of Cauchy interlacing)

Dependencies

Uses only names already present in StatsMLlib.LinearAlgebra.Matrix.CourantFischer:

  • ciSup_le, le_ciInf
  • rayleighQuotient, minRayleighQuotientOn, maxRayleighQuotientOn
  • equivMapOfInjective

Testing

lake build StatsMLlib.LinearAlgebra.Matrix.InterlacingPR succeeds on mathlib v4.33.0 (2723 jobs).

License

Apache-2.0

…ving embeddings (Cauchy interlacing core; tested on mathlib v4.33.0, Apache-2.0)
@tukamilano

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Looks good to me! Thanks!

@tukamilano
tukamilano merged commit b5893e8 into Lean-MoDS:main Sep 11, 2026
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