The Dirichlet Problem for an Elliptic Functional Differential Equation with the Compressed, Expanded, and Rotated Argument

Abstract: The paper is devoted to the Dirichlet problem in a plain bounded domain for a linear divergent-form second-order functional differential equation with the compressed (expanded) and rotated argument of the highest derivatives of the unknown function. Necessary and sufficient conditions for the Gårding-type inequality are obtained in algebraic form. The result may depend not only on the absolute value of the coefficients but also on their signature. Under some restrictions on the structure of the operator and the geometry of the domain, the questions of existence, uniqueness, and smoothness of generalized solutions are studied for all possible values of the coefficients and parameters of transformations in the equation, even when the equation is not strongly elliptic. © The Author(s) 2024.