arXiv subjects

Sergei Sitnik

Publications and source records attributed to Sergei Sitnik.

3 recordsLinked to original sources

arXiv2022

Inequalities in calculus: methods of prooving results and problem solving

This preprint is a text for students and teachers on inequalities. Some standard topics are covered on application of calculus to inequality proving. Many examples are considered, stated, solved or partially solved. Some problems are standard, but some are rare, new and original. The next topics are considered with many examples: monotonicity of functions, Lagrange theorem and inequalities proving, estimating of finite sums, inequalities of Schlömilch-LeMonnier type, proof of inequalities by method of mathematical induction, inequalities for the number $e$, exponentials, logarithmic and similar functions, some means and their inequalities, Cauchy-Bunyakovskii, Minkovskii, Young, Hölder (Rogers-Hölder-Riesz !) inequalities and some of their improvements and generalisations. Some new results include inequalities on exponentials, logarithmic and similar functions, generalisations of Cauchy--Bunyakovskii and Young inequalities, some mean inequalities including mean inequalities on the complex domain and more.

math.HO↗

arXiv2020

The explicit formula for solution of anomalous diffusion equation in the multi-dimensional space

This paper intends on obtaining the explicit solution of $n$-dimensional anomalous diffusion equation in the infinite domain with non-zero initial condition and vanishing condition at infinity. It is shown that this equation can be derived from the parabolic integro-differential equation with memory in which the kernel is $t^{-α}E_{1-α, 1-α}(-t^{1-α}),α\in(0, 1),$ where $E_{α, β}$ is the Mittag-Liffler function. Based on Laplace and Fourier transforms the properties of the Fox H-function and convolution theorem, explicit solution for anomalous diffusion equation is obtained.

math.CA↗

arXiv2020

Fractional powers of Bessel operator and its numerical calculation

The article discusses the fractional powers of the Bessel operator and their numerical implementation. An extensive literature is devoted to the study of fractional powers of the Laplace operator and their applications. Such degrees are used in the construction of functional spaces, in the natural generalization of the Schrödinger equation in quantum theory, in the construction of the models of acoustic wave propagation in complex media (for example, biological tissues) and space-time models of anomalous (very slow or very fast) diffusion, in spectral theory etc. If we assume the radiality of the function on which the Laplace operator acts, then we receive the problem of constructing the fractional power of the Bessel operator. We propose to use a compositional method for constructing the operators mentioned earlier, which leads to constructions similar in their properties to the Riesz derivatives. The Hankel transform is considered as a basic integral transformation. On its basis, the compositional method proposed by V.V. Katrakhov and S.M. Sitnik, negative powers of the Bessel operator are constructed. The resulting operator contains the Gaussian hypergeometric function in the kernel. For further study, the generalized translation operator is considered in the article, and its properties are proved. For constructing a positive fractional power of the Bessel operator known methods of regularization of the integral are considered. Then, a scheme for the numerical calculation of fractional powers of the Bessel operator is proposed. This scheme is based on the Taylor--Delsarte formula obtained by B.M. Levitan.

math.CA↗