valid approximation
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Boussinesq approximation (water waves) — In fluid dynamics, the Boussinesq approximation for water waves is an approximation valid for weakly non linear and fairly long waves. The approximation is named after Joseph Boussinesq, who first derived them in response to the observation by… … Wikipedia
Rotating wave approximation — The rotating wave approximation is an approximation used in atom optics and magnetic resonance. In this approximation, terms in a Hamiltonian which oscillate rapidly are neglected. This is a valid approximation when the applied electromagnetic… … Wikipedia
WKB approximation — In physics, the WKB (Wentzel–Kramers–Brillouin) approximation, also known as WKBJ (Wentzel–Kramers–Brillouin–Jeffreys) approximation, is the most familiar example of a semiclassical calculation in quantum mechanics in which the wavefunction is… … Wikipedia
Stirling's approximation — In mathematics, Stirling s approximation (or Stirling s formula) is an approximation for large factorials. It is named in honour of James Stirling.The formula is written as:n! approx sqrt{2pi n}, left(frac{n}{e} ight)^{n}.Roughly, this means that … Wikipedia
Slowly varying envelope approximation — In physics, the slowly varying envelope approximation (SVEA) is the assumption that the envelope of a forward travelling wave pulse varies slowly in time and space compared to a period or wavelength. This requires the spectrum of the signal to be … Wikipedia
Lanczos approximation — In mathematics, the Lanczos approximation is a method for computing the Gamma function numerically, published by Cornelius Lanczos in 1964. It is a practical alternative to the more popular Stirling s approximation for calculating the Gamma… … Wikipedia
Kirkwood approximation — The Kirkwood superposition approximation was introduced by Matsuda (2000) as a means of representing a discrete probability distribution. The name apparently refers to a 1942 paper by John G. Kirkwood. The Kirkwood approximation for a discrete… … Wikipedia
Potential flow — streamlines around a NACA 0012 airfoil at 11° angle of attack, with upper and lower streamtubes identified. In fluid dynamics, potential flow describes the velocity field as the gradient of a scalar function: the velocity potential. As a result,… … Wikipedia
Airy wave theory — In fluid dynamics, Airy wave theory (often referred to as linear wave theory) gives a linearised description of the propagation of gravity waves on the surface of a homogeneous fluid layer. The theory assumes that the fluid layer has a uniform… … Wikipedia
Singular perturbation — In mathematics, more precisely in perturbation theory, a singular perturbation problem is a problem containing a small parameter that cannot be approximated by setting the parameter value to zero. This is in contrast to regular perturbation… … Wikipedia
relativity — /rel euh tiv i tee/, n. 1. the state or fact of being relative. 2. Physics. a theory, formulated essentially by Albert Einstein, that all motion must be defined relative to a frame of reference and that space and time are relative, rather than… … Universalium
