Abstract
Given an objective function (differentiable or nondifferentiable), an important optimization problem is to find the global minimizer of the given function and a natural issue is to identify such functions with the global property. In this paper, we study real-valued functions defined on a Hilbert space and provide several sufficient conditions to ensure the existence of the global minimizer of such functions. For a proper lower semicontinuous function, we prove that a global minimizer can be guaranteed if it is bounded below, has the primal-lower-nice property and satisfies the generalized Palais-Smale condition. This result can cover the classic differentiable case whose proof depends heavily on the global existence of the ordinary differential equation. Several examples are constructed to show that the global minimizer may be violated if any of three conditions above is dropped.

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Acknowledgements
The authors wish to thank the referees for careful reading of the paper and for many valuable comments, which drew our attention to [8] and helped to improve our presentation.
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This research was supported by the National Natural Science Foundations of China (Grant Nos. 11991021, 12021001, 11971422, 11826204 and 11826206). Research of the third author was supported by CAS “Light of West China” Program and by Jointed Key Project of Yunnan Provincial Science and Technology Department and Yunnan University [No. 2018FY001014] and Program for Innovative Research Team (in Science and Technology) in Universities of Yunnan Province [No. C176240111009]
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Chen, L., Dai, YH. & Wei, Z. Sufficient conditions for existence of global minimizers of functions on Hilbert spaces. J Glob Optim 84, 137–147 (2022). https://doi.org/10.1007/s10898-022-01133-3
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DOI: https://doi.org/10.1007/s10898-022-01133-3
Keywords
- Sufficient condition
- Global minmizer
- Primal-lower-nice
- Subdifferential evolution problem
- Palais–Smale condition