Ulineære

Ulineære, often translated as nonlinear, is a term used to describe relationships, equations, or systems that do not conform to linear models. In mathematics, a function f is linear if it satisfies f(x + y) = f(x) + f(y) and f(c x) = c f(x) for all x, y and scalars c. Ulineære encompasses all functions and systems that violate at least one of these properties. Nonlinear models may still be simple, but their outputs are not proportional to inputs, and they do not exhibit the superposition property.

Examples of nonlinear relationships include polynomials of degree two or higher, exponential, logarithmic, and many trigonometric functions, as well as piecewise or saturating functions. In applied contexts, many differential equations are nonlinear, leading to rich and complex behaviors not present in linear models.

In systems theory, linear systems have constant parameters and obey superposition, which greatly simplifies analysis and design. Nonlinear systems can exhibit phenomena such as bifurcations, chaos, and sensitivity to initial conditions, making their behavior more difficult to predict and control.

Applications and methods: modeling real-world phenomena often requires nonlinear relationships. Solving nonlinear equations typically relies on iterative numerical methods (for example, Newton-Raphson) or simulation. Optimization problems are frequently nonlinear and can be nonconvex, containing multiple local optima.

Terminology: affine transformations are close to linear but include a constant offset and are not strictly linear. The concept of nonlinearity is central across mathematics, physics, economics, and computer science.