English

Generalized Koch curves and Thue-Morse sequences

Dynamical Systems 2021-10-04 v1 Metric Geometry

Abstract

Let (tn)n0(t_n)_{n\ge0} be the well konwn ±1\pm1 Thue-Morse sequence +1,1,1,+1,1,+1,+1,1,.+1,-1,-1,+1,-1,+1,+1,-1,\cdots. Since the 1982-1983 work of Coquet and Dekking, it is known that k<ntke2kπi3\sum_{k<n}t_ke^\frac{2k\pi i}{3} is strongly related to the famous Koch curve. As a natural generalization, for integer m1m\ge1, we use k<nδke2kπim\sum_{k<n}\delta_ke^\frac{2k\pi i}{m} to define generalized Koch curve, where (δn)n0(\delta_n)_{n\ge0} is the generalized Thue-Morse sequence defined to be the unique fixed point of the morphism +1+1,+δ1,,+δm+1\mapsto+1,+\delta_1,\cdots,+\delta_m 11,δ1,,δm-1\mapsto-1,-\delta_1,\cdots,-\delta_m beginning with δ0=+1\delta_0=+1 and δ1,,δm{+1,1}\delta_1,\cdots,\delta_m\in\{+1,-1\}, and we prove that generalized Koch curves are the attractors of corresponding iterated function systems. For the case that m2m\ge2, δ0==δm4=+1\delta_0=\cdots=\delta_{\lfloor\frac{m}{4}\rfloor}=+1, δm4+1==δmm41=1\delta_{\lfloor\frac{m}{4}\rfloor+1}=\cdots=\delta_{m-\lfloor\frac{m}{4}\rfloor-1}=-1 and δmm4==δm=+1\delta_{m-\lfloor\frac{m}{4}\rfloor}=\cdots=\delta_m=+1, the open set condition holds, and then the corresponding generalized Koch curve has Hausdorff, packing and box dimension log(m+1)/logk=0mδke2kπim\log(m+1)/\log|\sum_{k=0}^m\delta_ke^{\frac{2k\pi i}{m}}|, where taking m=3m=3 and then δ0=+1,δ1=δ2=1,δ3=+1\delta_0=+1,\delta_1=\delta_2=-1,\delta_3=+1 will recover the result on the classical Koch curve.

Keywords

Cite

@article{arxiv.2009.14488,
  title  = {Generalized Koch curves and Thue-Morse sequences},
  author = {Yao-Qiang Li},
  journal= {arXiv preprint arXiv:2009.14488},
  year   = {2021}
}
R2 v1 2026-06-23T18:54:07.300Z