theoretical-computer-science / Trace reconstruction; deletion channels

Can worst-case trace reconstruction be done with polynomially many traces?

Theorem 1.1: for fixed s∈(0,1]s\in(0,1] and 0<c<1/(4log⁡2)0<c<1/(4\log 2), Tq,s(n)≥nclog⁡(q3log⁡n)T_{q,s}(n)\ge n^{c\log(q^3\log n)} eventually whenever q3log⁡n→∞q^3\log n\to\infty; so Tq(n)=nΩ(log⁡log⁡n)T_q(n)=n^{\Omega(\log\log n)} at every fixed qq, a negative answer to the polynomial question. Theorem 1.2: the minimum total variation between one-trace laws of distinct length-nn words is o(n−A)o(n^{-A}) for all AA. The companions give a matching-type upper side: quasipolynomial samples and bit complexity with a uniform decoder for known rational retention, and polynomial bounds when q≤n−εq\le n^{-\varepsilon}. A gap remains between log⁡T\log T of order log⁡nlog⁡log⁡n\log n\log\log n (lower) and a power of log⁡n\log n (upper); the exact complexity is not determined.

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theoretical-computer-scienceSep 24, 2026Significance 42/100Registry: lean checked

Can worst-case trace reconstruction be done with polynomially many traces?

Prior state unknown→disproved

Theorem 1.1: for fixed s∈(0,1]s\in(0,1] and 0<c<1/(4log⁡2)0<c<1/(4\log 2), Tq,s(n)≥nclog⁡(q3log⁡n)T_{q,s}(n)\ge n^{c\log(q^3\log n)} eventually whenever q3log⁡n→∞q^3\log n\to\infty; so Tq(n)=nΩ(log⁡log⁡n)T_q(n)=n^{\Omega(\log\log n)} at every fixed qq, a negative answer to the polynomial question. Theorem 1.2: the minimum total variation between one-trace laws of distinct length-nn words is o(n−A)o(n^{-A}) for all AA. The companions give a matching-type upper side: quasipolynom…

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Theorem 1.1: for fixed s∈(0,1]s\in(0,1] and 0<c<1/(4log⁡2)0<c<1/(4\log 2), Tq,s(n)≥nclog⁡(q3log⁡n)T_{q,s}(n)\ge n^{c\log(q^3\log n)} eventually whenever q3log⁡n→∞q^3\log n\to\infty; so Tq(n)=nΩ(log⁡log⁡n)T_q(n)=n^{\Omega(\log\log n)} at every fixed qq, a negative answer to the polynomial question. Theorem 1.2: the minimum total variation between one-trace laws of distinct length-nn words is o(n−A)o(n^{-A}) for all AA. The companions give a matching-type upper side: quasipolynomial samples and bit complexity with a uniform decoder for known rational retention, and polynomial bounds when q≤n−εq\le n^{-\varepsilon}. A gap remains between log⁡T\log T of order log⁡nlog⁡log⁡n\log n\log\log n (lower) and a power of log⁡n\log n (upper); the exact complexity is not determined.

Theorem 1.1: for fixed s∈(0,1]s\in(0,1] and 0<c<1/(4log⁡2)0<c<1/(4\log 2), Tq,s(n)≥nclog⁡(q3log⁡n)T_{q,s}(n)\ge n^{c\log(q^3\log n)} eventually whenever q3log⁡n→∞q^3\log n\to\infty; so Tq(n)=nΩ(log⁡log⁡n)T_q(n)=n^{\Omega(\log\log n)} at every fixed qq, a negative answer to the polynomial question. Theorem 1.2: the minimum total variation between one-trace laws of distinct length-nn words is o(n−A)o(n^{-A}) for all AA. The companions give a matching-type upper side: quasipolynomial samples and bit complexity with a uniform decoder for known rational retention, and polynomial bounds when q≤n−εq\le n^{-\varepsilon}. A gap remains between log⁡T\log T of order log⁡nlog⁡log⁡n\log n\log\log n (lower) and a power of log⁡n\log n (upper); the exact complexity is not determined.

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