Abstract
This paper presents a novel, general-purpose interface for adding interactive human-in-the-loop steering controls to existing simulation codes. The design is agnostic to any specific in situ analysis and visualization library, though our reference implementation is based on Ascent - a common in situ visualization and analysis library for large-scale simulations. Traditional in situ analysis and visualization workflows are typically automated through trigger mechanisms that execute as simulations reach certain predefined states (e.g. every N timesteps, simulation parameters become unstable, etc.). Although such automated in situ tasks suffice for many real-world applications, we demonstrate that a complementary interactive interface can significantly boost scientific productivity. We show through two use cases how our approach enables scientists to pause simulations and make interactive adjustments between timesteps. This method eliminates cold restart overhead, accelerating setup, troubleshooting, and exploration.