One Concave-Convex Inequality and Its Consequences

Our starting point is an integral inequality that involves convex, concave and monotonically increasing functions. We provide some interpretations of the inequality, in terms of both probability and terms of linear functionals, from which we further generate completely monotone functions and means. The latter application is seen from the perspective of monotonicity and convexity.

On Complete Monotonicity of Solution to the Fractional Relaxation Equation with the nth Level Fractional Derivative

In this paper, we first deduce the explicit formulas for the projector of the nth level fractional derivative and for its Laplace transform. Afterwards, the fractional relaxation equation with the nth level fractional derivative is discussed. It turns out that, under some conditions, the solutions to the initial-value problems for this equation are completely monotone functions that can be represented in form of the linear combinations of the Mittag–Leffler functions with some power law weights. Special attention is given to the case of the relaxation equation with the second level derivative.

Approximation of and by completely monotone functions

We investigate convergence in the cone of completely monotone fu nctions. Particular attention is paid to the approximation of and by exponentials and stretched exponentials. The need for such an analysis is a consequence of the fact that although stretched exponentials can be approximated by sums of exponentials, exponentials cannot in general be approximated by sums of stretched exponentials. doi:10.1017/S1446181120000012

ON THE $ \langle \rho_j,W_j \rangle $ GENERALIZED COMPLETELY MONOTONE FUNCTIONS

We consider sequences $ {\lbrace \rho_j \rbrace}_{0}^{\infty} $ $ (\rho_0 \mathclose{=} 1, \rho_j \mathclose{\geq} 1) $, $ {\lbrace \alpha_j \rbrace}_{0}^{\infty} $ $ (\alpha_0 \mathclose{=} 1, \alpha_j \mathclose{=} 1 \mathclose{-} (1/\rho_j )) $, $ {\lbrace W_j (x) \rbrace}_{0}^{\infty} \mathclose{\in} W $, where $$ W \mathclose{=} \lbrace {\lbrace W_j (x) \rbrace}_{0}^{\infty} / W_0 (x) \mathclose{\equiv} 1, W_j (x) \mathclose{>} 0, {W}_{j}^{\prime} (x) \mathclose{\leq} 0, W_j (x) \mathclose{\in} C^\infty [0,a] \rbrace, $$ $ C^\infty [0,a] $ is the class of functions of infinitely differentiable. For such sequences we introduce systems of operators $ {\lbrace {A}_{a,n}^{\ast} f \rbrace}_{0}^{\infty} $, $ {\lbrace \tilde{A}_{a,n}^{\ast} f \rbrace}_{0}^{\infty} $ and functions $ {\lbrace {U}_{a,n} (x) \rbrace}_{0}^{\infty} $, $ {\lbrace {\Phi}_{n} (x,t) \rbrace}_{0}^{\infty} $. For a certain class of functions a generalization of Taylor–Maclaurin type formulae was obtained. We also introduce the concept of $ \langle \rho_j,W_j \rangle $ generalized completely monotone functions and establish a theorem on their representation.

A comment on a controversial issue: A generalized fractional derivative cannot have a regular kernel

The problem whether a given pair of functions can be used as the kernels of a generalized fractional derivative and the associated generalized fractional integral is reduced to the problem of existence of a solution to the Sonine equation. It is shown for some selected classes of functions that a necessary condition for a function to be the kernel of a fractional derivative is an integrable singularity at 0. It is shown that locally integrable completely monotone functions satisfy the Sonine equation if and only if they are singular at 0.

APPROXIMATION OF AND BY COMPLETELY MONOTONE FUNCTIONS

We investigate convergence in the cone of completely monotone functions. Particular attention is paid to the approximation of and by exponentials and stretched exponentials. The need for such an analysis is a consequence of the fact that although stretched exponentials can be approximated by sums of exponentials, exponentials cannot in general be approximated by sums of stretched exponentials.

A generation method for completely monotone functions

In this article we present technique how to produce completely monotone functions using linear functionals and already known families of completely monotone functions. After that, using mean value theorems, we construct means of Cauchy type that have monotonicity properties.

ON A GENERALIZED FORMULA OF TAYLOR–MACLAURIN TYPE ON THE GENERALIZED COMPLETELY MONOTONE FUNCTIONS

In the paper Taylor–Maclaurin type formulas for some classes of functions are obtained. The main result of this study introduces an idea of the generalized classes of $ \langle \rho_j \rangle $ completely monotone function. Under the various conditions $ \left( \sum\limits_{j=1}^{\infty} \dfrac{1}{\rho_j} < + \infty ,\ \sum\limits_{j=1}^{\infty} \dfrac{1}{\rho_j} = + \infty \right) $ the terms of their representation are obtained and some related theorems are proved.