Mironenko reflecting function
# Mironenko reflecting function

In applied mathematics, the reflecting function $\,F(t,x)$ of a differential system ${\dot {x}}=X(t,x)$ connects the past state Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "http://localhost:6011/en.wikipedia.org/v1/":): {\displaystyle \,x(-t)} of the system with the future state $\,x(t)$ of the system by the formula $\,x(-t)=F(t,x(t)).$ The concept of the reflecting function was introduced by Uladzimir Ivanavich Mironenka.

## Definition

For the differential system ${\dot {x}}=X(t,x)$ with the general solution $\varphi (t;t_{0},x)$ in Cauchy form, the Reflecting Function of the system is defined by the formula $F(t,x)=\varphi (-t;t,x).$

## Application

If a vector-function $X(t,x)$ is $\,2\omega$-periodic with respect to $\,t$, then $\,F(-\omega ,x)$ is the in-period $\,[-\omega ;\omega ]$ transformation (Poincaré map) of the differential system ${\dot {x}}=X(t,x).$ Therefore the knowledge of the Reflecting Function give us the opportunity to find out the initial dates $\,(\omega ,x_{0})$ of periodic solutions of the differential system ${\dot {x}}=X(t,x)$ and investigate the stability of those solutions.

For the Reflecting Function $\,F(t,x)$ of the system ${\dot {x}}=X(t,x)$ the basic relation

    $\,F_{t}+F_{x}X+X(-t,F)=0,\qquad F(0,x)=x.$

is holding.

Therefore we have an opportunity sometimes to find Poincaré map of the non-integrable in quadrature systems even in elementary functions.

## Literature

* Мироненко В. И. Отражающая функция и периодические решения дифференциальных уравнений. — Минск, Университетское, 1986. — 76 с.
* Мироненко В. И. Отражающая функция и исследование многомерных дифференциальных систем. — Гомель: Мин. образов. РБ, ГГУ им. Ф. Скорины, 2004. — 196 с.
