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Project-declaredLean 4.31.0 · mathlib@fabf563a7c95

Scalar Vec Mul mul l2Norm Sq le

ArkLib.Lattices.CyclotomicModulus.scalarVecMul_mul_l2NormSq_le

Plain-language statement

Micciancio/Young product bound. Over the power-of-two cyclotomic modulus powTwoCyclotomic α (φ = X^{2^α}+1), scaling an already-c-scaled vector by a further ring element d of bounded centered ℓ₁ norm grows the squared ℓ₂ norm by at most κ² (the honest Young/Micciancio inequality ‖(c·d)·v‖₂² ≤ ‖d‖₁² · ‖c·v‖₂² over the negacyclic convolu...

Exact Lean statement

theorem scalarVecMul_mul_l2NormSq_le {cols : ℕ} (c d : Rq Φ) (v : PolyVec (Rq Φ) cols)
    {κ βSq : ℕ} (hd : Rq.l1Norm Φ d ≤ κ)
    (hv : vecL2NormSq Φ (scalarVecMul c v) ≤ βSq) :
    vecL2NormSq Φ (scalarVecMul (c * d) v) ≤ scalarVecMulMulL2NormSqBound κ βSq

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
theorem scalarVecMul_mul_l2NormSq_le {cols : } (c d : Rq Φ) (v : PolyVec (Rq Φ) cols)    {κ βSq : } (hd : Rq.l1Norm Φ d  κ)    (hv : vecL2NormSq Φ (scalarVecMul c v)  βSq) :    vecL2NormSq Φ (scalarVecMul (c * d) v)  scalarVecMulMulL2NormSqBound κ βSq := by  unfold vecL2NormSq scalarVecMulMulL2NormSqBound  have hcomm :  i, scalarVecMul (c * d) v i = d * scalarVecMul c v i := by    intro i; simp only [scalarVecMul_apply]; ring  calc ∑ i, Rq.l2NormSq Φ (scalarVecMul (c * d) v i)      = ∑ i, Rq.l2NormSq Φ (d * scalarVecMul c v i) := by simp_rw [hcomm]    _  ∑ i, (Rq.l1Norm Φ d) ^ 2 * Rq.l2NormSq Φ (scalarVecMul c v i) :=        Finset.sum_le_sum fun i _ => Rq.l2NormSq_mul_le:= α) d (scalarVecMul c v i)    _ = (Rq.l1Norm Φ d) ^ 2 * ∑ i, Rq.l2NormSq Φ (scalarVecMul c v i) := by rw [ Finset.mul_sum]    _  κ ^ 2 * βSq := Nat.mul_le_mul (Nat.pow_le_pow_left hd 2) hv
Project
ArkLib
License
Apache-2.0
Commit
fad5cbf80877
Source
ArkLib/Data/Lattices/CyclotomicRing/NormBounds/MicciancioYoung.lean:325-337

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Plain-language statement

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Project-declaredLean 4.31.0

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Plain-language statement

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