Rq l2Norm Sq mul le
ArkLib.Lattices.CyclotomicModulus.Rq.l2NormSq_mul_le
Plain-language statement
Per-entry product norm bound (Micciancio/Young, cf. [Mic07, ineqs. (2.6)–(2.7)]). Over the negacyclic ring X^{2^α}+1, ‖d·w‖₂² ≤ ‖d‖₁²·‖w‖₂².
Exact Lean statement
theorem Rq.l2NormSq_mul_le (d w : Rq Φ) :
Rq.l2NormSq Φ (d * w) ≤ (Rq.l1Norm Φ d) ^ 2 * Rq.l2NormSq Φ wFormal artifact
Lean source
theorem Rq.l2NormSq_mul_le (d w : Rq Φ) : Rq.l2NormSq Φ (d * w) ≤ (Rq.l1Norm Φ d) ^ 2 * Rq.l2NormSq Φ w := by have hAzero : ∀ i, 2 ^ α ≤ i → (d.1.coeff i).valMinAbs = 0 := by intro i hi have hc : d.1.coeff i = 0 := by rw [CompPoly.CPolynomial.coeff_toPoly] refine Polynomial.coeff_eq_zero_of_degree_lt (lt_of_lt_of_le ((Φ).degree_toPoly_lt_of_reduced d.2) ?_) rw [hachi_degree, hachi_natDegree]; exact_mod_cast hi rw [hc, ZMod.valMinAbs_zero] have hBzero : ∀ j, 2 ^ α ≤ j → (w.1.coeff j).valMinAbs = 0 := by intro j hj have hc : w.1.coeff j = 0 := by rw [CompPoly.CPolynomial.coeff_toPoly] refine Polynomial.coeff_eq_zero_of_degree_lt (lt_of_lt_of_le ((Φ).degree_toPoly_lt_of_reduced w.2) ?_) rw [hachi_degree, hachi_natDegree]; exact_mod_cast hj rw [hc, ZMod.valMinAbs_zero] have hc : ∀ k ∈ Finset.range (2 ^ α), (((d * w).1.coeff k).valMinAbs.natAbs : ℤ) ≤ ∑ i ∈ Finset.range (2 ^ α), ((d.1.coeff i).valMinAbs.natAbs : ℤ) * ((w.1.coeff ((k + 2 ^ α - i) % (2 ^ α))).valMinAbs.natAbs : ℤ) := by intro k hk have hkn : k < 2 ^ α := Finset.mem_range.mp hk have hnat : ((d * w).1.coeff k).valMinAbs.natAbs ≤ ∑ i ∈ Finset.range (2 ^ α), ((d.1.coeff i).valMinAbs).natAbs * ((w.1.coeff ((k + 2 ^ α - i) % (2 ^ α))).valMinAbs).natAbs := by refine le_trans (valMinAbs_natAbs_le ((∑ p ∈ Finset.antidiagonal k, (d.1.coeff p.1).valMinAbs * (w.1.coeff p.2).valMinAbs) - ∑ p ∈ Finset.antidiagonal (2 ^ α + k), (d.1.coeff p.1).valMinAbs * (w.1.coeff p.2).valMinAbs) ?_) (natAbs_conv_le (by positivity) k hkn (fun i => (d.1.coeff i).valMinAbs) (fun j => (w.1.coeff j).valMinAbs) hAzero hBzero) rw [Int.cast_sub, cast_conv (α := α) d w k, cast_conv (α := α) d w (2 ^ α + k), ← coeff_mul_rq_two_block (α := α) d w hkn] exact_mod_cast hnat have key := sum_conv_sq_le (n := 2 ^ α) (fun i => ((d.1.coeff i).valMinAbs.natAbs : ℤ)) (fun j => ((w.1.coeff j).valMinAbs.natAbs : ℤ)) (fun k => (((d * w).1.coeff k).valMinAbs.natAbs : ℤ)) (fun i => by positivity) (fun j => by positivity) (fun k => by positivity) hc have e1 : (Rq.l2NormSq Φ (d * w) : ℤ) = ∑ k ∈ Finset.range (2 ^ α), (((d * w).1.coeff k).valMinAbs.natAbs : ℤ) ^ 2 := by simp only [Rq.l2NormSq]; rw [hachi_natDegree]; push_cast; rfl have e2 : (Rq.l1Norm Φ d : ℤ) = ∑ i ∈ Finset.range (2 ^ α), ((d.1.coeff i).valMinAbs.natAbs : ℤ) := by simp only [Rq.l1Norm]; rw [hachi_natDegree]; push_cast; rfl have e3 : (Rq.l2NormSq Φ w : ℤ) = ∑ j ∈ Finset.range (2 ^ α), ((w.1.coeff j).valMinAbs.natAbs : ℤ) ^ 2 := by simp only [Rq.l2NormSq]; rw [hachi_natDegree]; push_cast; rfl have hgoal : (Rq.l2NormSq Φ (d * w) : ℤ) ≤ ((Rq.l1Norm Φ d : ℤ)) ^ 2 * (Rq.l2NormSq Φ w : ℤ) := by rw [e1, e2, e3]; exact key exact_mod_cast hgoal- Project
- ArkLib
- License
- Apache-2.0
- Commit
- fad5cbf80877
- Source
- ArkLib/Data/Lattices/CyclotomicRing/NormBounds/MicciancioYoung.lean:261-315
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