Inductive Domain Transfer In Misspecified Simulation-Based Inference

Simulation-based inference (SBI) of latent parameters in physical systems is often hindered by model misspecification-the mismatch between simulated and real-world observations caused by inherent modeling simplifications. RoPE, a recent SBI approach, addresses this challenge through a two-stage domain transfer process that combines semi-supervised calibration with optimal transport (OT)based distribution alignment. However, RoPE operates in a fully transductive setting, requiring access to a batch of test samples at inference time, which limits scalability and generalization. We propose a fully inductive and amortized SBI framework that integrates calibration and distributional alignment into a single, end-to-end trainable model called FRISBI. Our method leverages mini-batch OT with a closed-form coupling to align real and simulated observations that correspond to the same latent parameters, using both paired calibration data and unpaired samples. A conditional normalizing flow is then trained to approximate the OTinduced posterior, enabling efficient inference without simulation access at test time. Across a range of synthetic and real-world benchmarks-including complex medical biomarker estimation-our approach matches or exceeds the performance of RoPE, while offering improved scalability and applicability in challenging, misspecified environments.