Research map / Learning theory and algorithms / Optimal transport
Log-Averaged Mirror Prox for Fast, Large-Scale Optimal Transport in Linear Space
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Proposes LAMP, a linear-space (O(n+m) memory) dual-only implementation of primal-dual mirror prox for OT/EOT that is equivalent to PDMP, with a last-iterate certificate for direct unregularized OT and GPU-optimized log-domain reductions.
Problem
Large-scale (entropic) optimal transport requires O(nm) storage for primal-dual first-order methods with good last-iterate complexity, which is prohibitive for large n, m and hard to map to GPUs.
Approach
Shows that primal mirror descent steps on the row-stochastic reparameterized OT penalty equal dual log-averaging with a temperature-annealing scalar sequence, so primal iterates can be recovered from O(n+m) dual variables, keeping PDMP's guarantees while using dense GPU reductions.
Key results
- LAMP (eta=0) outperforms Sinkhorn-based baselines on DOTmark with l_inf and l_1 ground costs at n=m=4096, converging extremely rapidly; Sinkhorn overtakes it for l_2^2 costs with tuned regularization.
- A fused+warp-tiled LogSumExp kernel runs 252.5 ms vs PyKeOps 332 ms at n=65536 on an RTX 4090.
- LAMP runs 512x512 color transfer on a single L40s using about 38 MB, where explicit primal-dual methods would need about 512 GB; scales to n=m=2^18.
Surprising findings
- Unregularized LAMP with eta=0 and fixed step sizes performs competitively without problem-specific tuning, outperforming well-tuned Sinkhorn variants on several cost types.
Limitations
- Last-iterate convergence (infeasibility) for the performant eta=0 regime is not proven; the paper only gives a bound dependent on infeasibility.
- LAMP converges slowly for l_2^2 costs where ||C||_inf = O(n), and Sinkhorn can overtake it.
- Theoretical complexity guarantees hold only for the conservative eta>0 parameter set.
Experimental setup
Datasets: DOTmark cell omics datasets
Benchmarks: DOTmark cell omics similarity color transfer 512x512
Metrics: objective gap plus infeasibility primal-dual gap wall-clock time infeasibility
Baselines: Sinkhorn APDAMD Accelerated Sinkhorn Bregman HPD Annealed Sinkhorn Dual Extrapolation PyKeOps
Builds on: PDMP mirror prox Sinkhorn Round (Altschuler et al.) Dual extrapolation
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