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Description:
My PhD thesis deals with Chebyshev-Grüss- and Ostrowski-type inequalities in the univariate and bivariate case. Such inequalities have drawn much attention in recent years due to their applications. The classical form of Grüss' inequality, first published by G. Grüss in 1935, gives an estimate of the difference between the integral of the product and the product of the integrals of two functions in C[a,b]. In the following years a lot of variants of this inequality appeared in the literature. This talk consists of five parts. The first part includes a motivation, containing some introductory instruments that are further used to obtain the results. In the second section, Chebyshev-Grüss-type inequalities in the one-dimensional case are of interest. The results are introduced with the help of second moments, first absolute moments and quantities over differences of second and first moments. They are applied to (positive) linear operators. Oscillations which are expressed by the least concave majorant of the first order modulus are used in the first place. The use of such oscillations includes all points in the considered interval, and that is the reason why a new approach arises looking at fewer points. When talking about discrete oscillations, Chebyshev-Grüss-type inequalities for more than two functions are obtained at the end of this section. The third section extends the results from the univariate to the bivariate case. The method of parametric extensions by means of product of two compact metric spaces is used. Applications are given for both the approach with the least concave majorant and also for the one via discrete oscillations. The purpose of the fourth and fifth sections is to complete this study, in the sense that univariate and bivariate Ostrowski-type inequalities are also considered. Some applications are specified and Ostrowski type inequalities are obtained, with or without the participation of the iterates of the operators. The limit of the iterates of positive linear operators is also studied. ...