  Recent advances in both theory and computational power have created
opportunities to simulate biomolecular processes more efficiently using
adaptive ensemble simulations. Ensemble simulations are now widely used to
compute a number of individual simulation trajectories and analyze statistics
across them. Adaptive ensemble simulations offer a further level of
sophistication and flexibility by enabling high-level algorithms to control
simulations based on intermediate results. We review some of the adaptive
ensemble algorithms and software infrastructure currently in use and outline
where the complexities of implementing adaptive simulation have limited
algorithmic innovation to date. We describe an adaptive ensemble API to
overcome some of these barriers and more flexibly and simply express adaptive
simulation algorithms to help realize the power of this type of simulation.
