On the Iteration Complexity of Oblivious First-Order Optimization Algorithms

Yossi Arjevani, Ohad Shamir
Proceedings of The 33rd International Conference on Machine Learning, PMLR 48:908-916, 2016.

Abstract

We consider a broad class of first-order optimization algorithms which are \emphoblivious, in the sense that their step sizes are scheduled regardless of the function under consideration, except for limited side-information such as smoothness or strong convexity parameters. With the knowledge of these two parameters, we show that any such algorithm attains an iteration complexity lower bound of Ω(\sqrtL/ε) for L-smooth convex functions, and \tildeΩ(\sqrtL/μ\ln(1/ε)) for L-smooth μ-strongly convex functions. These lower bounds are stronger than those in the traditional oracle model, as they hold independently of the dimension. To attain these, we abandon the oracle model in favor of a structure-based approach which builds upon a framework recently proposed in Arjevani et al. (2015). We further show that without knowing the strong convexity parameter, it is impossible to attain an iteration complexity better than \tildeΩ\sqrt(L/μ)\ln(1/ε). This result is then used to formalize an observation regarding L-smooth convex functions, namely, that the iteration complexity of algorithms employing time-invariant step sizes must be at least Ω(L/ε).

Cite this Paper

BibTeX
@InProceedings{pmlr-v48-arjevani16, title = {On the Iteration Complexity of Oblivious First-Order Optimization Algorithms}, author = {Arjevani, Yossi and Shamir, Ohad}, booktitle = {Proceedings of The 33rd International Conference on Machine Learning}, pages = {908--916}, year = {2016}, editor = {Balcan, Maria Florina and Weinberger, Kilian Q.}, volume = {48}, series = {Proceedings of Machine Learning Research}, address = {New York, New York, USA}, month = {20--22 Jun}, publisher = {PMLR}, pdf = {http://proceedings.mlr.press/v48/arjevani16.pdf}, url = {https://proceedings.mlr.press/v48/arjevani16.html}, abstract = {We consider a broad class of first-order optimization algorithms which are \emphoblivious, in the sense that their step sizes are scheduled regardless of the function under consideration, except for limited side-information such as smoothness or strong convexity parameters. With the knowledge of these two parameters, we show that any such algorithm attains an iteration complexity lower bound of Ω(\sqrtL/ε) for L-smooth convex functions, and \tildeΩ(\sqrtL/μ\ln(1/ε)) for L-smooth μ-strongly convex functions. These lower bounds are stronger than those in the traditional oracle model, as they hold independently of the dimension. To attain these, we abandon the oracle model in favor of a structure-based approach which builds upon a framework recently proposed in Arjevani et al. (2015). We further show that without knowing the strong convexity parameter, it is impossible to attain an iteration complexity better than \tildeΩ\sqrt(L/μ)\ln(1/ε). This result is then used to formalize an observation regarding L-smooth convex functions, namely, that the iteration complexity of algorithms employing time-invariant step sizes must be at least Ω(L/ε).} }
Endnote
%0 Conference Paper %T On the Iteration Complexity of Oblivious First-Order Optimization Algorithms %A Yossi Arjevani %A Ohad Shamir %B Proceedings of The 33rd International Conference on Machine Learning %C Proceedings of Machine Learning Research %D 2016 %E Maria Florina Balcan %E Kilian Q. Weinberger %F pmlr-v48-arjevani16 %I PMLR %P 908--916 %U https://proceedings.mlr.press/v48/arjevani16.html %V 48 %X We consider a broad class of first-order optimization algorithms which are \emphoblivious, in the sense that their step sizes are scheduled regardless of the function under consideration, except for limited side-information such as smoothness or strong convexity parameters. With the knowledge of these two parameters, we show that any such algorithm attains an iteration complexity lower bound of Ω(\sqrtL/ε) for L-smooth convex functions, and \tildeΩ(\sqrtL/μ\ln(1/ε)) for L-smooth μ-strongly convex functions. These lower bounds are stronger than those in the traditional oracle model, as they hold independently of the dimension. To attain these, we abandon the oracle model in favor of a structure-based approach which builds upon a framework recently proposed in Arjevani et al. (2015). We further show that without knowing the strong convexity parameter, it is impossible to attain an iteration complexity better than \tildeΩ\sqrt(L/μ)\ln(1/ε). This result is then used to formalize an observation regarding L-smooth convex functions, namely, that the iteration complexity of algorithms employing time-invariant step sizes must be at least Ω(L/ε).
RIS
TY - CPAPER TI - On the Iteration Complexity of Oblivious First-Order Optimization Algorithms AU - Yossi Arjevani AU - Ohad Shamir BT - Proceedings of The 33rd International Conference on Machine Learning DA - 2016/06/11 ED - Maria Florina Balcan ED - Kilian Q. Weinberger ID - pmlr-v48-arjevani16 PB - PMLR DP - Proceedings of Machine Learning Research VL - 48 SP - 908 EP - 916 L1 - http://proceedings.mlr.press/v48/arjevani16.pdf UR - https://proceedings.mlr.press/v48/arjevani16.html AB - We consider a broad class of first-order optimization algorithms which are \emphoblivious, in the sense that their step sizes are scheduled regardless of the function under consideration, except for limited side-information such as smoothness or strong convexity parameters. With the knowledge of these two parameters, we show that any such algorithm attains an iteration complexity lower bound of Ω(\sqrtL/ε) for L-smooth convex functions, and \tildeΩ(\sqrtL/μ\ln(1/ε)) for L-smooth μ-strongly convex functions. These lower bounds are stronger than those in the traditional oracle model, as they hold independently of the dimension. To attain these, we abandon the oracle model in favor of a structure-based approach which builds upon a framework recently proposed in Arjevani et al. (2015). We further show that without knowing the strong convexity parameter, it is impossible to attain an iteration complexity better than \tildeΩ\sqrt(L/μ)\ln(1/ε). This result is then used to formalize an observation regarding L-smooth convex functions, namely, that the iteration complexity of algorithms employing time-invariant step sizes must be at least Ω(L/ε). ER -
APA
Arjevani, Y. & Shamir, O.. (2016). On the Iteration Complexity of Oblivious First-Order Optimization Algorithms. Proceedings of The 33rd International Conference on Machine Learning, in Proceedings of Machine Learning Research 48:908-916 Available from https://proceedings.mlr.press/v48/arjevani16.html.

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