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Abstract

We introduce underworld3, a finite element, solid-Earth modelling code designed to be both straightforward to use and highly scalable to peak high-performance computing environments. underworld3 inherits the design patterns of earlier versions of underworld such as 1) A python user interface that is inherently safe for parallel computation. 2) A symbolic interface that allows users to construct and simplify combinations of functions, unknowns and gradients-of-unknowns on the fly that are then used to construct the finite element representation of the problem. 3) Fast, robust, parallel numerical solvers, 4) Flexible, Lagrangian "particle" swarms for modeling transport-dominated quantities that are fully interchangeable with other data-types and can be treated as symbolic quantities. 5) Mesh adaptivity that falls fully within the symbolic framework. The design philosophy of Underworld is to provide readable python code that stays close to the mathematics of the problem definition and is scalable (unedited) from Jupyter notebooks all the way to tens of thousands of cores. Underworld is entirely open source and founded on open source computational frameworks. It provides an accessible entry point for anyone to begin modelling (on a laptop or a free cloud resource) and those models can easily be scaled-up to solve cutting edge problems of societal importance. Typical problems of interest are groundwater flow studies on a whole-of-basin scale, earthquake rupture models coupled with tectonic deformation with applications to hazards, ice-sheet flow and deformation, subduction zone models coupled to over-riding plate deformation, and stress modelling at the continental scale.