The dimension formula conjecture for self-similar measures

Let Φ\Phi be an iterated function system, let pp be a probability vector, and let μ\mu be the corresponding self-similar measure. The entropy rate is

h(Φ,p)=lim⁡N→∞1NH(X1∘⋯∘XN),h(\Phi,p)=\lim_{N\to\infty}\frac{1}{N}H(X_1\circ\cdots\circ X_N),

where X1,X2,…X_1,X_2,\ldots are independent random elements of Φ\Phi distributed according to pp, and HH denotes Shannon entropy. The dimension formula conjecture.

dim⁡μ=min⁡(1,h(Φ,p)∑i∈Λpilog⁡∣λi∣−1).\dim \mu=\min\left(1,\frac{h(\Phi,p)}{\sum_{i\in\Lambda}p_i\log|\lambda_i|^{-1}}\right).

This folklore conjecture predicts that the dimension is governed by the entropy rate, capped at the ambient dimension. It is motivated by the similarity dimensions obtained from iterated compositions and collapsing exact overlaps; no resolution status is supplied in the source.

References

Primary source

Péter P. Varjú, “Entropy rates in the dimension theory of self-similar measures”, arXiv:2509.22042 (2026).

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