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About the dichotomy of market "models" shown in the first reference, one could argue that for applied purposes it makes little practical difference, however from the fundamental (physics) vantage: EMH is a true underlying mechanism to generate the price series. On the other hand fractal properties of a price series is NOT the mechanism generating the series that shows it, it is a symptom (and an emergent one at that). The underlying mechanism can be something completely obscure (hence the _emergent_ nature of fractals). Equivalently, fGBM (fractional Geometric Brownian Motion) is only a statistical description of the process and manifestly has nothing to show us about the underlying mechanism.

Most such mechanisms involve memory which makes reasonable sense in the context of markets. Here is a good, easy read on the fGBM:

https://doi.org/10.1016/j.aej.2020.10.023

But it is yet another case where finance takes ideas from physics without real understanding of their applicability: in their specific case, they obtain a null result in that they get precisely what a I might expect: randomness for large time scales (e.g. their choice of monthly price series) in the form of H=0.5 ("Hurst exponent"). Had they done their physics lab homework, they'd have done proper error analysis and see that all their results are consistent with H=1/2 i.e. diffusion and no memory=> no exploitable property for trading.

The reason for the latter statement is worthwhile to note because it is also the most important thing to remember about the fractals: The fractal properties are just a facet of (Pareto-)Levy-distributions (aka stable-distributions).

Hard enough as Levy-distributions are to work with, in the case of markets, it is even messier because the actual distribution is a "Truncated-Levy distribution", meaning the fat-tails (linear on the log-log-scale) hit a wall and crash to -infinity on the log-log-scale (zero on the linear scale). The only upside of that added mess being that the truncation of the hitherto fat-tails (<=>trends) results in loss of "stability" and thus the applicability of the central-limit theorem. which says: 1) infinitely long trends do not exist and 2) over long-enough time-intervals, the distributions tend to the normal-distribution (the most special member of the Levy-stable family) which results from ANY underlying mechanism that is truly random (completely unpredictable): aka, diffusion.

Thus an important take-away for the practitioner is: if any, try to exploit the fractal properties in not-too-long observation intervals.

Fractals were all the rage around the turn of the century. A fellow named Edgar Peters sold a zillion copies of a book which was utterly useless to anyone interested in exploiting the fractal properties of markets, and surely they DO EXIST. Once folks found out it is a tough nut to crack and of very little applicability, the interest died down quickly. To see people still spending time on it is a bit surprising...

Dr Nguyen: thanks for the post, it was entertaining for me as fractals were a point of departure for me back in the mid-1990's for from pure physics to the applied side. Here are the best two results (on the applied side) from my multi-year journey culminated in:

https://www.researchgate.net/publication/227498207_Mathematical_fortune-telling

and

https://www.researchgate.net/publication/397720545_AI_in_Finance_price_Forecasting_3

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