Min Wt ge of MDS
CoreResults.minWt_ge_of_MDS
Plain-language statement
Every nonzero codeword in a code generated by a k × n MDS matrix has Hamming weight greater or equal to n - k + 1.
Exact Lean statement
lemma minWt_ge_of_MDS [Field F] [DecidableEq F] {G : Matrix (Fin k) (Fin n) F}
(hMDS : Matrix.IsMDS G) {c : Fin n → F} (hc_mem : c ∈ fromRowGenMat G) (hc_ne : c ≠ 0) :
n - k + 1 ≤ hammingNorm cFormal artifact
Lean source
lemma minWt_ge_of_MDS [Field F] [DecidableEq F] {G : Matrix (Fin k) (Fin n) F}(hMDS : Matrix.IsMDS G) {c : Fin n → F} (hc_mem : c ∈ fromRowGenMat G) (hc_ne : c ≠ 0) : n - k + 1 ≤ hammingNorm c := by have h_hamming_norm : n - Finset.card (Finset.filter (fun j => c j = 0) Finset.univ) ≥ n - k + 1 := by rcases le_or_gt k (Finset.card (Finset.filter (fun j => c j = 0) Finset.univ)) with h | h <;> simp only [ge_iff_le, Order.add_one_le_iff] · have h_contra : ∃ σ : Fin k ↪ Fin n, ∀ j, c (σ j) = 0 := by obtain ⟨s, hs⟩ : ∃ s : Finset (Fin n), s.card = k ∧ ∀ j ∈ s, c j = 0 := by exact Exists.elim (Finset.exists_subset_card_eq h) fun s hs => ⟨s, hs.2, fun j hj => Finset.mem_filter.mp ( hs.1 hj ) |>.2⟩ exact ⟨⟨fun j => s.orderEmbOfFin (by aesop) j, fun j j' h => by aesop⟩, fun j => hs.2 _ (by aesop)⟩ obtain ⟨σ, hσ⟩ := h_contra have h_det : Matrix.det (Matrix.submatrix G id σ) = 0 := by have h_contra : ∃ v : Fin k → F, v ≠ 0 ∧ Matrix.vecMul v (Matrix.submatrix G id σ) = 0 := by obtain ⟨v, hv⟩ := hc_mem refine ⟨v, ?_, ?_⟩ <;> contrapose! hc_ne <;> simp_all +decide [funext_iff, Matrix.vecMul] grind exact Matrix.exists_vecMul_eq_zero_iff.mp h_contra; have := hMDS σ aesop · refine Nat.sub_lt_sub_left ?_ h by_contra h_contra exact hc_ne (funext fun j => by_contradiction fun hj => h_contra <| lt_of_lt_of_le (Finset.card_lt_card <| Finset.filter_ssubset.mpr ⟨j, by aesop⟩) <| by simp only [Finset.card_univ, Fintype.card_fin, le_refl]) convert h_hamming_norm.le using 1 simp [hammingNorm, Finset.filter_not, Finset.card_sdiff]- Project
- ArkLib
- License
- Apache-2.0
- Commit
- fad5cbf80877
- Source
- ArkLib/Data/CodingTheory/Basic/MDSCode.lean:37-66
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This lemma proves the final algebraic step in the DG25 Theorem 3.1 proof. It shows that if R > e + 1, then e * (R / (R - 1)) < e + 1. The intuition is that the fraction R / (R - 1) is always greater than 1, but as R gets larger, it gets closer to 1. The hypothesis R > e + 1 provides a strong enough bound to ensure the product e * (fraction) do...
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Source project: ArkLib
Person-level attribution pending.
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Plain-language statement
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Source project: ArkLib
Person-level attribution pending.