Author(s): Carlos Romero Rocha; Nicolas Renaud; Koen Leijnse; Samuel Van Beek; Mario Castro-Gama
Linked Author(s): Koen Leijnse
Keywords: Least-Cost Design Newton-Raphson Global-Gradient-Algorithm Quantum Computing Water Distribution Network Modelling
Abstract: To compute models for Water Distribution Networks (WDN), a large system of non-linear equations needs to be solved and the hallmark algorithm for computing these models is the Newton-Raphson Global Gradient Algorithm (NR-GGA), which solves these systems iteratively. Even so, large networks can take multiple days to model and the complexity of networks is only expected to increase towards the future. It is therefore important to explore different algorithms using innovative technologies, to improve the tractability of modelling large networks. Quantum computing is such an innovative technology that is still in its early stages of development, paired with a different computational paradigm. In this research we have determined the feasibility of using quantum computing as a subroutine of NR-GGA and for replacing NR-GGA in its entirety. Calculations were run on emulators of gate-based quantum computers and using simulated annealing and models were computed for small 2-loop networks of 7 nodes. To improve NR-GGA, three different quantum subroutines were used: the hybrid Variational Quantum Linear Solver (VQLS) showed the best results on this small data-set. To replace NR-GGA by a quantum algorithm in its entirety, we also used a QA-based approach for simulating higher-order polynomials to determine the Least-Cost Design (LCD) of a small 3 node network.
Year: 2025