risk allocation
Risk-Bounded Multi-Agent Visual Navigation via Iterative Risk Allocation
Parimi, Viraj, Williams, Brian C.
Safe navigation is essential for autonomous systems operating in hazardous environments, especially when multiple agents must coordinate using only high-dimensional visual observations. While recent approaches successfully combine Goal-Conditioned RL (GCRL) for graph construction with Conflict-Based Search (CBS) for planning, they typically rely on static edge pruning to enforce safety. This binary strategy is overly conservative, precluding feasible missions that require traversing high-risk regions, even when the aggregate risk is acceptable. To address this, we introduce a framework for Risk-Bounded Multi-Agent Path Finding (\problem{}), where agents share a user-specified global risk budget ($Δ$). Rather than permanently discarding edges, our framework dynamically distributes per-agent risk budgets ($δ_i$) during search via an Iterative Risk Allocation (IRA) layer that integrates with a standard CBS planner. We investigate two distribution strategies: a greedy surplus-deficit scheme for rapid feasibility repair, and a market-inspired mechanism that treats risk as a priced resource to guide improved allocation. This yields a tunable trade-off wherein agents exploit available risk to secure shorter, more efficient paths, but revert to longer, safer detours under tighter budgets. Experiments in complex visual environments show that, our dynamic allocation framework achieves higher success rates than baselines and effectively leverages the available safety budget to reduce travel time.
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Conformal Prediction in The Loop: A Feedback-Based Uncertainty Model for Trajectory Optimization
Conformal Prediction (CP) is a powerful statistical machine learning tool to construct uncertainty sets with coverage guarantees, which has fueled its extensive adoption in generating prediction regions for decision-making tasks, e.g., Trajectory Optimization (TO) in uncertain environments. However, existing methods predominantly employ a sequential scheme, where decisions rely unidirectionally on the prediction regions, and consequently the information from decision-making fails to be fed back to instruct CP. In this paper, we propose a novel Feedback-Based CP (Fb-CP) framework for shrinking-horizon TO with a joint risk constraint over the entire mission time. Specifically, a CP-based posterior risk calculation method is developed by fully leveraging the realized trajectories to adjust the posterior allowable risk, which is then allocated to future times to update prediction regions. In this way, the information in the realized trajectories is continuously fed back to the CP, enabling attractive feedback-based adjustments of the prediction regions and a provable online improvement in trajectory performance. Furthermore, we theoretically prove that such adjustments consistently maintain the coverage guarantees of the prediction regions, thereby ensuring provable safety. Additionally, we develop a decision-focused iterative risk allocation algorithm with theoretical convergence analysis for allocating the posterior allowable risk which closely aligns with Fb-CP. Furthermore, we extend the proposed method to handle distribution shift. The effectiveness and superiority of the proposed method are demonstrated through benchmark experiments.
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Multivariate Systemic Risk Measures and Computation by Deep Learning Algorithms
Doldi, Alessandro, Feng, Yichen, Fouque, Jean-Pierre, Frittelli, Marco
In this work we propose deep learning-based algorithms for the computation of systemic shortfall risk measures defined via multivariate utility functions. We discuss the key related theoretical aspects, with a particular focus on the fairness properties of primal optima and associated risk allocations. The algorithms we provide allow for learning primal optimizers, optima for the dual representation and corresponding fair risk allocations. We test our algorithms by comparison to a benchmark model, based on a paired exponential utility function, for which we can provide explicit formulas. We also show evidence of convergence in a case for which explicit formulas are not available.
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Distributionally Robust RRT with Risk Allocation
Ekenberg, Kajsa, Renganathan, Venkatraman, Olofsson, Björn
An integration of distributionally robust risk allocation into sampling-based motion planning algorithms for robots operating in uncertain environments is proposed. We perform non-uniform risk allocation by decomposing the distributionally robust joint risk constraints defined over the entire planning horizon into individual risk constraints given the total risk budget. Specifically, the deterministic tightening defined using the individual risk constraints is leveraged to define our proposed exact risk allocation procedure. Our idea of embedding the risk allocation technique into sampling based motion planning algorithms realises guaranteed conservative, yet increasingly more risk feasible trajectories for efficient state space exploration.
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Chance-Constrained Trajectory Optimization for High-DOF Robots in Uncertain Environments
Dawson, Charles, Jasour, Ashkan, Hofmann, Andreas, Williams, Brian
Many practical applications of robotics require systems that can operate safely despite uncertainty. In the context of motion planning, two types of uncertainty are particularly important when planning safe robot trajectories. The first is environmental uncertainty -- uncertainty in the locations of nearby obstacles, stemming from sensor noise or (in the case of obstacles' future locations) prediction error. The second class of uncertainty is uncertainty in the robots own state, typically caused by tracking or estimation error. To achieve high levels of safety, it is necessary for robots to consider both of these sources of uncertainty. In this paper, we propose a risk-bounded trajectory optimization algorithm, known as Sequential Convex Optimization with Risk Optimization (SCORA), to solve chance-constrained motion planning problems despite both environmental uncertainty and tracking error. Through experiments in simulation, we demonstrate that SCORA significantly outperforms state-of-the-art risk-aware motion planners both in planning time and in the safety of the resulting trajectories.
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Chance-constrained Static Schedules for Temporally Probabilistic Plans
Fang, Cheng (Massachusetts Institute of Technology) | Wang, Andrew J. (MIT) | Williams, Brian C. (CSAIL, MIT)
Time management under uncertainty is essential to large scale projects. From space exploration to industrial production, there is a need to schedule and perform activities. given complex specifications on timing. In order to generate schedules that are robust to uncertainty in the duration of activities, prior work has focused on a problem framing that uses an interval-bounded uncertainty representation. However, such approaches are unable to take advantage of known probability distributions over duration. In this paper we concentrate on a probabilistic formulation of temporal problems with uncertain duration, called the probabilistic simple temporal problem. As distributions often have an unbounded range of outcomes, we consider chance-constrained solutions, with guarantees on the probability of meeting temporal constraints. By considering distributions over uncertain duration, we are able to use risk as a resource, reason over the relative likelihood of outcomes, and derive higher utility solutions. We first demonstrate our approach by encoding the problem as a convex program. We then develop a more efficient hybrid algorithm whose parent solver generates risk allocations and whose child solver generates schedules for a particular risk allocation. The child is made efficient by leveraging existing interval-bounded scheduling algorithms, while the parent is made efficient by extracting conflicts over risk allocations. We perform numerical experiments to show the advantages of reasoning over probabilistic uncertainty, by comparing the utility of schedules generated with risk allocation against those generated from reasoning over bounded uncertainty. We also empirically show that solution time is greatly reduced by incorporating conflict-directed risk allocation.
Human-Robot Team Coordination with Dynamic and Latent Human Task Proficiencies: Scheduling with Learning Curves
Liu, Ruisen, Natarajan, Manisha, Gombolay, Matthew
As robots become ubiquitous in the workforce, it is essential that human-robot collaboration be both intuitive and adaptive. A robot's quality improves based on its ability to explicitly reason about the time-varying (i.e. learning curves) and stochastic capabilities of its human counterparts, and adjust the joint workload to improve efficiency while factoring human preferences. We introduce a novel resource coordination algorithm that enables robots to explore the relative strengths and learning abilities of their human teammates, by constructing schedules that are robust to stochastic and time-varying human task performance. We first validate our algorithmic approach using data we collected from a user study (n = 20), showing we can quickly generate and evaluate a robust schedule while discovering the latest individual worker proficiency. Second, we conduct a between-subjects experiment (n = 90) to validate the efficacy of our coordinating algorithm. Results from the human-subjects experiment indicate that scheduling strategies favoring exploration tend to be beneficial for human-robot collaboration as it improves team fluency (p = 0.0438), while also maximizing team efficiency (p < 0.001).
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Chance-Constrained Path Planning with Continuous Time Safety Guarantees
Ariu, Kaito (The University of Tokyo) | Fang, Cheng (Massachusetts Institute of Technology) | Arantes, Marcio (Universidade de Sao Paulo) | Toledo, Claudio (Universidade de Sao Paulo) | Williams, Brian (Massachusetts Institute of Technology)
We extend chance-constrained path planning with direct method into continuous time. Chance-constrained path planning is a method to obtain the optimal path satisfying a specified risk (or probability of failure) value. Previous work expects trajectories' states as discrete information with respect to time. This discretized encoding makes the conversion from probabilistic path planning to deterministic path planning easy. However, risk guarantees are only produced for the discrete time model. The probability of constraints violation in continuous time could be larger than the discretized risk values. To address this problem, we modified the constraint encoding and risk assessment method. First, we introduce a computationally efficient mean path securing method, which uses fewer binary variables as compared with prior work. Second, we note that the deviation of the actual trajectory from the mean trajectory can be considered as a Brownian motion, for which the reflection principle holds in general. Therefore, we take advantage of the reflection principle to bound the probability of the constraint violation in continuous time. In numerical simulations, we confirmed faster solution generation, and the probability guarantees of the path in the continuous time model, with deterioration in the objective function.
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Risk-Aware Scheduling throughout Planning and Execution
Wang, Andrew J. (Massachusetts Institute of Technology)
Scheduling is integral to many real-world logistics problems. It can be as simple as catching the bus in the morning, or as complex as assembling a commercial airliner. While simple applications render scheduling tools trivial, these tools have not been widely adopted for complex scenarios either. The larger the scenario, the greater the temporal uncertainty throughout the system, and many schedulers do not consider the probabilistic uncertainty in actions' durations. Figure 1: The role of scheduling in a plannning and execution This makes them brittle to temporal disturbances or architecture. In this architecture, the planner and scheduler first generate Figure 1 diagrams the layers of reasoning for a planning executive a plan and scheduling policy offline, which the dispatcher to map logistical goals into real-world actions.
Resolving Over-Constrained Probabilistic Temporal Problems through Chance Constraint Relaxation
Yu, Peng (Massachusetts Institute of Technology) | Fang, Cheng (Massachusetts Institute of Technology) | Williams, Brian (Massachusetts Institute of Technology)
When scheduling tasks for field-deployable systems, our solutions must be robust to the uncertainty inherent in the real world. Although human intuition is trusted to balance reward and risk, humans perform poorly in risk assessment at the scale and complexity of real world problems. In this paper, we present a decision aid system that helps human operators diagnose the source of risk and manage uncertainty in temporal problems. The core of the system is a conflict-directed relaxation algorithm, called Conflict-Directed Chance-constraint Relaxation (CDCR), which specializes in resolving over-constrained temporal problems with probabilistic durations and a chance constraint bounding the risk of failure. Given a temporal problem with uncertain duration, CDCR proposes execution strategies that operate at acceptable risk levels and pinpoints the source of risk. If no such strategy can be found that meets the chance constraint, it can help humans to repair the over-constrained problem by trading off between desirability of solution and acceptable risk levels. The decision aid has been incorporated in a mission advisory system for assisting oceanographers to schedule activities in deep-sea expeditions, and demonstrated its effectiveness in scenarios with realistic uncertainty.
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