See Linear constitutive equations and Nonlinear correlation functions. The earliest methods for solving quadratic equations were geometric. Babylonian cuneiform tablets contain problems reducible to solving quadratic equations. Linearization is another technique for solving nonlinear equations. The matrix exponential has applications to systems of linear differential equations. PDEs find their generalisation in stochastic partial differential equations. Euler's notation is useful for stating and solving linear differential equations. It is used to solve systems of linear differential equations. Sanderson has uploaded series on topics including linear algebra, calculus, differential equations, and neural networks. There are several algorithms for solving a system of linear equations. Another application of matrices is in the solution of systems of linear equations. Solving this system of linear equations for and yields . These matrices can be used in the Kalman filter equations. His dissertation was about singularities in analytic partial differential equations. Math is more than formulas and equations.