The study demonstrates that certain constants are not reached in binary-input channels, suggesting novel implications for information theory.
We prove that for binary-input channels with common output support, the Jensen-Shannon SDPI contraction coefficient η_JSD(W) is not attained by any fixed pair of input distributions. The ratio JSD(PW||QW)/JSD(P,Q) equals a weighted average of a strictly concave contraction function C(t), forcing strict inequality. The supremum is approached only by diagonal sequences. Using edge reduction (Ordentlich-Polyanskiy 2022), we extend this to all finite-input full-support channels.
No takes yet. Share an insight, caveat, or question.
Alex Shvets (2026) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: