life$^x$ - heart module: a high-performance simulator for the cardiac function. Package 1: Fiber generation

Modeling the whole cardiac function involves several complex multi-physics and multi-scale phenomena that are highly computationally demanding, which makes calling for simpler yet accurate, high-performance computational tools still a paramount challenge to be addressed. Despite all the efforts made by several research groups worldwide, no software has progressed as a standard reference tool for whole-heart fully-coupled cardiac simulations in the scientific community yet. In this work we present the first publicly released package of the heart module of life$^x$, a high-performance solver for multi-physics and multi-scale problems, aimed at cardiac applications. The goal of life$^x$ is twofold. On the one side, it aims at making in silico experiments easily reproducible and accessible to the wider public, targeting also users with a background in medicine or bio-engineering, thanks to an extensive documentation and user guide. On the other hand, being conceived as an academic research library, life$^x$ can be exploited by scientific computing experts to explore new modeling and numerical methodologies within a robust development framework. life$^x$ has been developed with a modular structure and will be released bundled in different modules/packages. This initial release includes a generator for myocardial fibers based on Laplace-Dirichlet-Rule-Based-Methods (LDRBMs). This report comes with an extensive technical and mathematical documentation to welcome new users to the core structure of a prototypical life$^x$ application and to provide with them a possible approach to include the generated cardiac fibers into more sophisticated computational pipelines.