Abstract
A local convergence result for an abstract descent method is proved. The sequence of iterates is attracted by a local (or global) minimum, stays in its neighborhood, and converges within this neighborhood. This result allows algorithms to exploit local properties of the objective function. In particular, the abstract theory in this paper applies to the inertial forward–backward splitting method: iPiano—a generalization of the Heavy-ball method. Moreover, it reveals an equivalence between iPiano and inertial averaged/alternating proximal minimization and projection methods. Key for this equivalence is the attraction to a local minimum within a neighborhood and the fact that, for a prox-regular function, the gradient of the Moreau envelope is locally Lipschitz continuous and expressible in terms of the proximal mapping. In a numerical feasibility problem, the inertial alternating projection method significantly outperforms its non-inertial variants.
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Notes
For the exact statements, we provide accurate references.
The error is measured after projecting the current iterate to the set of rank R matrices.
The heuristic version of Douglas–Rachford splitting in [39] guarantees boundedness of the iterates. We set \(\gamma =150\gamma _0\) and update \(\gamma \) by \(\max (\gamma /2,0.9999\gamma _0)\) if \(\Vert y^k- y^{k-1} \Vert _{} > t/k\). We refer to [39] for the meaning of \(y^k\). Since the proposed value \(t=1000\) did not work well in our experiment, we optimized t manually. \(t=75\) worked best.
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Communicated by Regina S. Burachik.
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Ochs, P. Local Convergence of the Heavy-Ball Method and iPiano for Non-convex Optimization. J Optim Theory Appl 177, 153–180 (2018). https://doi.org/10.1007/s10957-018-1272-y
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DOI: https://doi.org/10.1007/s10957-018-1272-y
Keywords
- Inertial forward–backward splitting
- Non-convex feasibility
- Prox-regularity
- Gradient of Moreau envelopes
- Heavy-ball method
- Alternating projection
- Averaged projection
- iPiano