Red-Black Heuristics for Planning Tasks with Conditional Effects

Red-black planning is a state-of-the-art approach to satisficing classical planning. Red-black planning heuristics are at the heart of the planner Mercury, the runner-up of a satisficing track in the International Planning Competition (IPC) 2014 and a major component of four additional planners in IPC 2018, including Saarplan, the runner-up in the agile track. Mercury’s exceptional performance is amplified by the fact that conditional effects were handled by the planner in a trivial way, simply by compiling them away. Conditional effects, however, are important for classical planning, and many domains require them for efficient modeling.Consequently, we investigate the possibility of handling conditional effects directly in the red-black planning heuristic function, extending the algorithm for computing red-black plans to the conditional effects setting. We show empirically that red-black planning heuristics that handle conditional effects natively outperform the variants that compile this feature away, improving coverage on tasks where black variables exist by 19%.