The strong convergence of a proximal pointalgorithm in complete CAT(0) metric spaces

The strong convergence of a proximal pointalgorithm in complete CAT(0) metric spaces

In this paper, we consider a proximal point algorithm for finding zeros of maximal mono-tone operators in complete CAT(0) spaces. First, a necessary and sufficient condition ispresented for the zero set of the operator to be nonempty. Afterwards, we prove that, un-der suitable conditions, the proposed algorithm converges strongly to the metric projectionof some point onto the zero set of the involving maximal monotone operator.

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  • [1]P. Ahmadi and H. Khatibzadeh,On the convergence of inexact proximal point algo-rithm on Hadamard manifolds, Taiwanese J. Math.18, 419–433, 2014.
  • [2]B. Ahmadi Kakavandi,Weak topologies in complete CAT(0) metric spaces, Proc.Amer. Math. Soc.141, 1029–1039, 2013.
  • [3]B. Ahmadi Kakavandi and M. Amini,Duality and subdifierential for convex functionson complete CAT(0) metric spaces, Nonlinear Anal.73, 3450–3455, 2010.
  • [4]M. Bacak,Convex analysis and optimization in Hadamard spaces, De Gruyter Seriesin Nonlinear Analysis and Applications,22, De Gruyter, Berlin, 2014.
  • [5]I.D. Berg and I.G. Nikolaev,Quasilinearization and curvature of Alexandrov spaces,Geom. Dedicata,133, 195–218, 2008.
  • [6]H. Br ́ezis and P.L. Lions,Produits infinis de r ́esolvantes, Israel J. Math.29, 329–345,1978.
  • [7]M. Bridson and A. Haefliger,Metric spaces of non-positive curvature,319, Springer,Berlin, 1999.
  • [8]K.S. Brown,Buildings, Springer, New York, 1989.
  • [9]D. Burago, Y. Burago and S. Ivanov,A course in metric geometry, Graduate Studiesin Mathematics,33American Mathematical Society, Providence, RI, 2001.
  • [10]H. Dehghan and J. Rooin,Metric projection and convergence theorems for nonexpan-sive mappings in Hadamard spaces, arXiv: 1410.1137v1[math.FA].
  • [11]S. Dhompongsa and B. Panyanak,On△-convergence theorems in CAT(0) spaces,Comput. Math. Appl.56, 2572–2579, 2008.
  • [12]B. Djafari Rouhani and H. Khatibzadeh,On the proximal point algorithm, J. Optim.Theory Appl.137, 411–417, 2008.
  • [13]B. Djafari Rouhani and S. Moradi, Strong convergence of two proximal point algo-rithms with possible unbounded error sequences, J. Optim.Theory Appl.172, 222–235,2017.
  • [14]R. Esp ́inola and A. Fern ́andez-Le ́on,CAT(k)-spaces, weak convergence and fixedpoints, J. Math. Anal. Appl.353, 410–427, 2009.
  • [15]K. Goebel and S. Reich,Uniform convexity, hyperbolic geometry, and nonexpan-sive mappings. Monographs and Textbooks in Pure and Applied Mathematics, MarcelDekker Inc., New York, 1984.
  • [16]M. Gromov and S.M. Bates,Metric structures for Riemannian and non-Riemannianspaces, Progress in Mathematics,152, eds. J. Lafontaine and P. Pansu) (Birkh ̈auser,Boston, 1999, with appendices by M. Katz, P. Pansu and S. Semmes.
  • [17]O. G ̈uler,On the convergence of the proximal point algorithm for convex minimization,SIAM J. Control Optim.29, 403–419, 1991.
  • [18]M.T. Heydari and S. Ranjbar,Halpern-type proximal point algorithm in completeCAT(0) metric spaces, An. St. Univ. Ovidius Constanta.24(3), 141–159, 2016.
  • [19]J. J ̈ost,Nonpositive curvature: geometric and analytic aspects, Lectures in Mathe-matics, Birkh ̈auser, Basel, 1997.
  • [20]H. Khatibzadeh and S. Ranjbar,Monotone operators and the proximal point algorithmin complete CAT(0) metric spaces, J. Aust. Math. Soc.103(1), 70–90, 2017.
  • [21]W.A. Kirk,Fixed point theorems in CAT(0) spaces andR-trees, J. Fixed Point TheoryAppl.4, 309–316, 2004.
  • [22]W.A. Kirk and B. Panyanak,A concept of convergence in geodesic spaces, NonlinearAnal. (TMA)68, 3689–3696, 2008.
  • [23]C. Li, G. L ́opez and V. Mart ́in-M ́arquez,Monotone vector fields and the proximalpoint algorithm on Hadamard manifolds, J. London Math. Soc.79(2), 663–683,2009.[24]T.C. Lim,Remarks on some fixed point theorems, Proc. Amer. Math. Soc.60, 179–182, 1976.
  • [25]B. Martinet, R ́egularisation d,in ́equations variationnelles par approximations succes-sives, Rev. Fran ́caise d,Inform. et de Rech. Op ́erationnelle,3, 154–158, 1970.
  • [26]R.T. Rockafellar,Monotone operators and the proximal point algorithm, SIAM J.Control Optim.14, 877–898, 1976.