Fixed Point Theory

Convergence of the Mann and Ishikawa type iterations.

Results on the equivalence of the convergence of certain iterations have been obtained.

• B.E. Rhoades and Ş.M. Şoltuz, The equivalence between Mann-Ishikawa iterations and multistep iteration, Nonlinear Analysis: Theory, Methods & Applications, 58 (2004) no. 1-2, 219-228.
• B.E. Rhoades and Ş.M. Şoltuz, The equivalence between the convergences of Ishikawa and Mann iterations for asymptotically nonexpansive in the intermediate sense and strong successively pseudocontractive maps, J. Math. Anal. Appl. 289 (2004), 266-278.
• B.E. Rhoades and Ş.M. Şoltuz, The equivalence between the convergences of Ishikawa and Mann iterations for asymptotically pseudocontractive map, J. Math. Anal. Appl. 283 (2003), 681-688.
• B.E. Rhoades, Ş.M . Şoltuz, The equivalence between T-stabilities of Mann and Ishikawa iterations, J. Math. Anal. Appl. 318 (2006), 472-475.

Local convergence of the successive approximations.

The high convergence orders of the successive approximations were characterized, an estimation of the attraction balls were obtained, and some results on the acceleration of the convergence of the successive approximations are given in:

• E. Cătinaş, On the superlinear convergence of the successive approximations method, J. Optim. Theory Appl., 113 (2002) no. 3, pp. 473-485.
• E. Cătinaş, Estimating the radius of an attraction ball, Appl. Math. Lett., 22 (2009) no. 5, pp. 712-714.
• E. Cătinaş, On accelerating the convergence of the successive approximations method, Rev. Anal. Numér. Théor. Approx., 30 (2001) no. 1, pp. 3-8.
• E. Cătinaş, How many steps still left to x*?, SIAM Rev. 63 (2021) no. 3, pp. 585–624.

Solutions of differential equations as fixed points.

In this direction we obtained existence, uniqueness results, data dependence and Ulam stability for the solution of functional-differential equations, differential equations with delays and mixed type argument.

• D. Otrocol, I.A. Rus, Functional-differential equations with “maxima” via weakly Picard operators theory, Bull. Math. Soc. Sci. Math. Roumanie, 51(99) 2008, no. 3, 253-261.
• D. Otrocol, I.A. Rus, Functional-differential equations with maxima of mixed type, Fixed Point Theory, 9 (2008) no. 1, 207-220.
• D. Otrocol, V.A. Ilea, Ulam stability for a delay differential equation, Central European Journal of Mathematics, 11 (2013) no. 7, 1296-1303.

The convergence of the sequence of the successive approximation by using contraction principle and step method with a weaker Lipschitz condition and a new algorithm of successive approximation sequence generated by the step method were obtained in

• V. Ilea, D. Otrocol, M.-A. Şerban and D. Trif, Integro-differential equation with two time lags, Fixed Point Theory, 13 (2012), no. 1, pp. 85-97.