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Is there a way to compute minimum distance of a code given a systematic parity check matrix? I know that min dist is smallest number $d$ such that there exists $d$ linearly dependant columns. I am looking in particular to find minimum distance of binary (codes over $\mathbb{F}_{2^l}$) quasi-cyclic of rate q/q+1. Parity check matrix for such codes have a structure $H=[I|C_1|C_2|...|C_m]$ where each $C_¡$ is a from class of circulant matrices. It may be useful that one can treat these codes as modules. Or even if there are any approximate algoruihms for this ?

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    $\begingroup$ Since you can take any code, and find a systematic parity check matrix for an equivalent code, the complexity class of this problem doesn't depend on whether there's a systematic parity check matrix or not. $\endgroup$ – Peter Shor May 5 at 1:20
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The problem for an arbitrary binary code is NP-hard.

Reference: Alexander Vardy, “The Intractability of Computing the Minimum Distance of a Code,” IEEE Trans. Inf. Thy., Vol. 43 pp. 1757--1766.

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  • $\begingroup$ Shot anything in particular for QC codes or may be an approximate algorithm for finding minimum distance. What I am looking for is a way to construct QC codes with high minimum distance. So even algorithms giving lower bounds (non-trivial) are worth a try. $\endgroup$ – Root May 5 at 4:13

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