Tighter Bounds for Structured Estimation

Part of Advances in Neural Information Processing Systems 21 (NIPS 2008)

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Olivier Chapelle, Chuong B., Choon Teo, Quoc Le, Alex Smola


Large-margin structured estimation methods work by minimizing a convex upper bound of loss functions. While they allow for efficient optimization algorithms, these convex formulations are not tight and sacrifice the ability to accurately model the true loss. We present tighter non-convex bounds based on generalizing the notion of a ramp loss from binary classification to structured estimation. We show that a small modification of existing optimization algorithms suffices to solve this modified problem. On structured prediction tasks such as protein sequence alignment and web page ranking, our algorithm leads to improved accuracy.