Jain's incidence-code parameter conjecture for unit graphs

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Let nn be a natural number, let G(Zn)G(\mathbb{Z}_n) be a unit graph, and let HH be a ∣V∣×∣E∣|V|\times|E| incidence matrix of G(Zn)G(\mathbb{Z}_n). Let ϕ(n)\phi(n) denote Euler's totient function, and let Cq(H)C_q(H) denote the code generated by HH over the finite field Fq\mathbb{F}_q. Jain's incidence-code conjecture. If 2∈U(Zn)2\in U(\mathbb{Z}_n), then the binary code generated by HH is

C2(H)=[(n−1)ϕ(n)2,n−1,ϕ(n)−1]2C_2(H)=\left[\frac{(n-1)\phi(n)}{2}, n-1, \phi(n)-1\right]_2

over F2\mathbb{F}_2. If 2∈NU(Zn)2\in N_U(\mathbb{Z}_n), then, for any odd prime qq, the qq-ary code generated by HH is

Cq(H)=[nϕ(n)2,n−1,ϕ(n)]qC_q(H)=\left[\frac{n\phi(n)}{2}, n-1, \phi(n)\right]_q

over Fq\mathbb{F}_q.

This conjecture specifies the length, dimension, and minimum distance of incidence-matrix codes associated with unit graphs. The surrounding paper states that it resolves this coding-theoretic conjecture from Jain2023, so this candidate is treated as solved.

References

Primary source

Apurba Sarkar, Kalyan Hansda and Makhan Maji, “Linear Codes Derived from the Structure of Unit Graphs Over Z_n”, arXiv:2503.03421 (2025).

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