\'s 1921 paper
Marquardt's 1921 paper, titled "Variationsrechnung", describes the Newton-Raphson Method of Iterative Approximations to a Solution of a System of Non-Linear Equations. The paper is composed of three parts: Part 1, titled "Grundlagen der Variationsrechnung" (Foundations of the Calculus of Variations), covers the basics of the calculus used to solve variational problems. Part 2, titled "Allgemeine Methode der Variationsrechnung" (General Method of the Calculus of Variations), goes into more detail as to the nature of variational problems and their solutions. Finally, Part 3, titled "Iterative Verfahren zur Lösung eines Systems von n Nichtlinearen Gleichungen" (Iterative Procedures to Solve a System of n Nonlinear Equations), describes Marquardt's Newton-Raphson Method for solving such systems of equations.