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This paper proposes a method to efficiently compute the voltage and current along a transmission line which can be “damaged”; that is its electrical properties can be unevenly distributed. The method approximates a transmission line by a self-similar circuit network and leverages our previous work regarding the frequency response for that class of networks. The main motivation arises from research for railway track circuit systems where transmission line models are often employed. Determining deviations from baseline properties of the railway circuit is important for health monitoring of the system and furthermore, changes in circuit properties due to a train occupying a segment of the track also is of great interest as a means to ensure safety. Thus, in addition to monitoring the integrity of the railway circuit, our approach also could provide a means for safe operation in that it can be used to detect segments of the rail system that are occupied by trains. 

Abstract Large-scale dynamical systems, no matter whether possessing interconnected appearances, are frequently modeled as networks. For instance, graphs, multi-agent systems, and materials' intricate behaviors are often treated as networked dynamical systems. However, only a few studies have approached the problem in the frequency domain, mostly due to the complexity of evaluating their frequency response. That gap is filled by this paper, which proposes algorithms computing a general class of self-similar networks' frequency response and transfer functions, no matter they are finite or infinite, damaged or undamaged. In addition, this paper shows that for infinite self-similar networks, even when they are damaged, fractional-order and irrational dynamics naturally come into sight. Most importantly, this paper illustrates that for a network under different operating conditions, its frequency response would form a set of neighboring plants, which sets the basis of applying robust control methods to dynamic networks. 

Fractional calculus is an increasingly recognized important tool for modeling complicated dynamics in modern engineering systems. While, in some ways, fractional derivatives are a straight-forward generalization of integer-order derivatives that are ubiquitous in engineering modeling, in other ways the use of them requires quite a bit of mathematical expertise and familiarity with some mathematical concepts that are not in everyday use across the broad spectrum of engineering disciplines. In more colloquial terms, the learning curve is steep. While the authors recognize the need for fundamental competence in tools used in engineering, a computational tool that can provide an alternative means to compute fractional derivatives does have a useful role in engineering modeling. This paper presents the use of a symmetric neural network that is trained entirely on integer-order derivatives to provide a means to compute fractional derivatives. The training data does not contain any fractional-order derivatives at all, and is composed of only integer-order derivatives. The means by which a fractional derivative can be obtained is by requiring the neural network to be symmetric, that is, it is the composition of two identical sets of layers trained on integer-order derivatives. From that, the information contained in the nodes between the two sets of layers contains half-order derivative information