In fluid dynamics, the **Davey–Stewartson equation (DSE)** was introduced in a paper by A. Davey and Keith Stewartson (1974) to describe the evolution of a three-dimensional wave-packet on water of finite depth.

It is a system of partial differential equations for a complex (wave-amplitude) field and a real (mean-flow) field :

The DSE is an example of a soliton equation in 2+1 dimensions. The corresponding Lax representation for it is given in Boiti, Martina & Pempinelli (1995).

In 1+1 dimensions the DSE reduces to the nonlinear Schrödinger equation

Itself, the DSE is the particular reduction of the Zakharov–Schulman system. On the other hand, the equivalent counterpart of the DSE is the Ishimori equation.

The DSE is the result of a multiple-scale analysis of modulated nonlinear surface gravity waves, propagating over a horizontal sea bed.

The **sine-Gordon equation** is a nonlinear hyperbolic partial differential equation in 1 + 1 dimensions involving the d'Alembert operator and the sine of the unknown function. It was originally introduced by Edmond Bour (1862) in the course of study of surfaces of constant negative curvature as the Gauss–Codazzi equation for surfaces of curvature −1 in 3-space, and rediscovered by Frenkel and Kontorova (1939) in their study of crystal dislocations known as the Frenkel–Kontorova model. This equation attracted a lot of attention in the 1970s due to the presence of soliton solutions.

In mathematics, the **Korteweg–de Vries (KdV) equation** is a mathematical model of waves on shallow water surfaces. It is particularly notable as the prototypical example of an exactly solvable model, that is, a non-linear partial differential equation whose solutions can be exactly and precisely specified. KdV can be solved by means of the inverse scattering transform. The mathematical theory behind the KdV equation is a topic of active research. The KdV equation was first introduced by Boussinesq and rediscovered by Diederik Korteweg and Gustav de Vries (1895).

Second order linear partial differential equations (PDEs) are classified as either **elliptic**, hyperbolic, or parabolic. Any second order linear PDE in two variables can be written in the form

**Burgers' equation** or **Bateman–Burgers equation** is a fundamental partial differential equation occurring in various areas of applied mathematics, such as fluid mechanics, nonlinear acoustics, gas dynamics, traffic flow. The equation was first introduced by Harry Bateman in 1915 and later studied by Johannes Martinus Burgers in 1948.

The **superposition principle**, also known as **superposition property**, states that, for all linear systems, the net response caused by two or more stimuli is the sum of the responses that would have been caused by each stimulus individually. So that if input *A* produces response *X* and input *B* produces response *Y* then input produces response.

In optics, an **ultrashort pulse** of light is an electromagnetic pulse whose time duration is of the order of a picosecond or less. Such pulses have a broadband optical spectrum, and can be created by mode-locked oscillators. They are commonly referred to as ultrafast events. Amplification of ultrashort pulses almost always requires the technique of chirped pulse amplification, in order to avoid damage to the gain medium of the amplifier.

In theoretical physics, the (one-dimensional) **nonlinear Schrödinger equation** (**NLSE**) is a nonlinear variation of the Schrödinger equation. It is a classical field equation whose principal applications are to the propagation of light in nonlinear optical fibers and planar waveguides and to Bose-Einstein condensates confined to highly anisotropic cigar-shaped traps, in the mean-field regime. Additionally, the equation appears in the studies of small-amplitude gravity waves on the surface of deep inviscid (zero-viscosity) water; the Langmuir waves in hot plasmas; the propagation of plane-diffracted wave beams in the focusing regions of the ionosphere; the propagation of Davydov's alpha-helix solitons, which are responsible for energy transport along molecular chains; and many others. More generally, the NLSE appears as one of universal equations that describe the evolution of slowly varying packets of quasi-monochromatic waves in weakly nonlinear media that have dispersion. Unlike the linear Schrödinger equation, the NLSE never describes the time evolution of a quantum state. The 1D NLSE is an example of an integrable model.

In theoretical physics, **Nordström's theory of gravitation** was a predecessor of general relativity. Strictly speaking, there were actually *two* distinct theories proposed by the Finnish theoretical physicist Gunnar Nordström, in 1912 and 1913 respectively. The first was quickly dismissed, but the second became the first known example of a metric theory of gravitation, in which the effects of gravitation are treated entirely in terms of the geometry of a curved spacetime.

In physics, the **Fermi–Pasta–Ulam–Tsingou problem** or formerly the **Fermi–Pasta–Ulam problem** was the apparent paradox in chaos theory that many complicated enough physical systems exhibited almost exactly periodic behavior – called **Fermi–Pasta–Ulam–Tsingou recurrence** – instead of ergodic behavior.

In mathematics and physics, the **Kadomtsev–Petviashvili equation** – or **KP equation**, named after Boris Borisovich Kadomtsev and Vladimir Iosifovich Petviashvili – is a partial differential equation to describe nonlinear wave motion. The KP equation is usually written as:

In superconductivity, a **long Josephson junction** (LJJ) is a Josephson junction which has one or more dimensions longer than the Josephson penetration depth . This definition is not strict.

In mathematics, the **inverse scattering transform** is a method for solving some non-linear partial differential equations. It is one of the most important developments in mathematical physics in the past 40 years. The method is a non-linear analogue, and in some sense generalization, of the Fourier transform, which itself is applied to solve many linear partial differential equations. The name "inverse scattering method" comes from the key idea of recovering the time evolution of a potential from the time evolution of its scattering data: inverse scattering refers to the problem of recovering a potential from its scattering matrix, as opposed to the direct scattering problem of finding the scattering matrix from the potential.

The **Ishimori equation (IE)** is a partial differential equation proposed by the Japanese mathematician Ishimori (1984). Its interest is as the first example of a nonlinear spin-one field model in the plane that is integrable Sattinger, Tracy & Venakides.

Dispersionless limits of integrable partial differential equations (PDE) arise in various problems of mathematics and physics and have been intensively studied in recent literature. They typically arise when considering slowly modulated long waves of an integrable dispersive PDE system.

The **Prandtl–Glauert transformation** is a mathematical technique which allows solving certain compressible flow problems by incompressible-flow calculation methods. It also allows applying incompressible-flow data to compressible-flow cases.

In fluid dynamics, **Airy 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 mean depth, and that the fluid flow is inviscid, incompressible and irrotational. This theory was first published, in correct form, by George Biddell Airy in the 19th century.

In mathematics, the **method of steepest descent** or **stationary-phase method** or **saddle-point method** is an extension of Laplace's method for approximating an integral, where one deforms a contour integral in the complex plane to pass near a stationary point, in roughly the direction of steepest descent or stationary phase. The saddle-point approximation is used with integrals in the complex plane, whereas Laplace’s method is used with real integrals.

In mathematical physics and the theory of partial differential equations, the solitary wave solution of the form is said to be **orbitally stable** if any solution with the initial data sufficiently close to forever remains in a given small neighborhood of the trajectory of .

The **Estevez–Mansfield–Clarkson equation** is a nonlinear partial differential equation introduced by Pilar Estevez, Elizabeth Mansfield, and Peter Clarkson.

The **Kundu equation** is a general form of integrable system that is gauge-equivalent to the mixed nonlinear Schrödinger equation. It was proposed by Anjan Kundu. as

- Boiti, M.; Martina, L.; Pempinelli, F. (December 1995), "Multidimensional localized solitons",
*Chaos, Solitons & Fractals*,**5**(12): 2377–2417, arXiv: patt-sol/9311002 , Bibcode:1995CSF.....5.2377B, doi:10.1016/0960-0779(94)E0106-Y, ISSN 0960-0779 - Davey, A.; Stewartson, K. (1974), "On three dimensional packets of surface waves",
*Proc. R. Soc. A*,**338**(1613): 101–110, Bibcode:1974RSPSA.338..101D, doi:10.1098/rspa.1974.0076 - Sattinger, David H.; Tracy, C. A.; Venakides, S., eds. (1991),
*Inverse Scattering and Applications*, Contemporary Mathematics,**122**, Providence, RI: American Mathematical Society, ISBN 0-8218-5129-2, MR 1135850

- Davey-Stewartson_system at the dispersive equations wiki.

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