Nonlinear media are essential for nonlinear optics. Nonlinear data analysis is closely related to nonlinear system identification. Linear differential equations frequently appear as approximations to nonlinear equations. Linearization is another technique for solving nonlinear equations. Iterative methods are often the only choice for nonlinear equations. DSP can involve linear or nonlinear operations. Gradient descent can also be used to solve a system of nonlinear equations. Mason introduced both nonlinear and linear flow graphs. Quadratic programming is a particular type of nonlinear programming. Kinetic parameters are frequently determined from experimental data via nonlinear estimation. For example, application of linear analysis to nonlinear circuits should be justified separately. This allows often considering as linear systems that are nonlinear otherwise. Numerical models are used to simulate fully nonlinear dynamos. Feedback linearization is a common approach used in controlling nonlinear systems. Solitons are caused by a cancellation of nonlinear and dispersive effects in the medium.