The Multivariate Theory of Functional Connections: An n-Dimensional Constraint Embedding Technique Applied to Partial Differential Equations

Abstract: The Theory of Functional Connections (TFC) is a functional interpolation framework founded upon the so-called constrained expression: a functional that expresses the family of all possible functions that satisfy some user-specified, linear constraints. These constrained expressions can be utilized to transform constrained problems into unconstrained ones. The benefits of doing so include faster solution times, more accurate solutions, and more robust convergence. This dissertation contains a comprehensive, self-contained presentation of the TFC theory beginning with simple univariate point constraints and ending with general linear constraints in $n$-dimensions; relevant mathematical theorems and clarifying examples are included throughout the presentation to expand and solidify the reader's understanding. Furthermore, this dissertation describes how TFC can be applied to estimate differential equations' solutions, its primary application to date. In addition, comparisons with other state-of-the-art algorithms that estimate differential equations' solutions are included to showcase the advantages and disadvantages of the TFC approach. Lastly, the aforementioned concepts are leveraged to estimate solutions of differential equations from the field of flexible body dynamics.