The sum of (nonlinear) maximal monotone operators is reconsidered from the Yosida approximation and graph-convergence point of view. This leads to a new concept, called variational sum, which coincides with the classical (pointwise) sum when the classical sum happens to be maximal monotone. In the case of subdifferentials of convex lower semicontinuous proper functions, the variational sum is equal to the subdifferential of the sum of the functions. A general feature of the variational sum is to involve not only the values of the two operators at the given point but also their values at nearby points.

Contact details are reproduced from the original publication and may be historical.

H. Attouch

Laboratoire d’Analyse Convexe, Université Montpellier II, F-34095 Montpellier Cedex 5

J.-B. Baillon

Université Lyon I, F-69622 Villeurbanne Cedex.

M. Théra

LACO, URA 1586, Université de Limoges, F-87060 Limoges Cedex.

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H. Attouch, J.-B. Baillon, M. Théra. “Variational Sum of Monotone Operators.” Journal of Convex Analysis 1 (1994), No. 1, 1–29. https://doi.org/10.68381/jca01001