@ARTICLE{BergerAbsilJungersNesterov2020, author = "Guillaume O. Berger and P.-A. Absil and Raphaël M. Jungers and Yurii Nesterov", title = "On the Quality of First-Order Approximation of Functions with Hölder Continuous Gradient", journal = "Journal of Optimization Theory and Applications", volume = "185", pages = "17--33", year = 2020 }