Abstract
We provide explicit formulas for the Levi-Civita connection and Riemannian Hessian for a Riemannian manifold that is a quotient of a manifold embedded in an inner product space with a non-constant metric function. Together with a classical formula for projection, this allows us to evaluate Riemannian gradient and Hessian for several families of metrics on classical manifolds, including a family of metrics on Stiefel manifolds connecting both the constant and canonical ambient metrics with closed-form geodesics. Using these formulas, we derive Riemannian optimization frameworks on quotients of Stiefel manifolds, including flag manifolds, and a new family of complete quotient metrics on the manifold of positive-semidefinite matrices of fixed rank, considered as a quotient of a product of Stiefel and positive-definite matrix manifold with affine-invariant metrics. The method is procedural, and in many instances, the Riemannian gradient and Hessian formulas could be derived by symbolic calculus. The method extends the list of potential metrics that could be used in manifold optimization and machine learning.
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Acknowledgements
We are thankful to the editor and reviewers for their careful reading and helpful comments. Their work is essential to the publication of this paper. It is our sole responsibility for any remaining mistake. We would like to thank Professor Overton for his interest and very kind advice, our friend John Tillinghast and our family for their support in this project.
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Nguyen, D. Operator-Valued Formulas for Riemannian Gradient and Hessian and Families of Tractable Metrics in Riemannian Optimization. J Optim Theory Appl 198, 135–164 (2023). https://doi.org/10.1007/s10957-023-02242-z
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DOI: https://doi.org/10.1007/s10957-023-02242-z
Keywords
- Optimization
- Riemannian Hessian
- Stiefel
- Positive-definite
- Positive-semidefinite
- Flag manifold
- Machine learning