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The Helmholtz equation has a variety of applications in physics and other sciences, including the wave equation, the diffusion equation, and the Schrödinger equation for a free particle. In optics, the Helmholtz equation is the wave equation for the electric field. [1] The equation is named after Hermann von Helmholtz, who studied it in 1860. [2]
The Kirchhoff–Helmholtz integral combines the Helmholtz equation with the Kirchhoff integral theorem [1] to produce a method applicable to acoustics, [2] seismology [3] and other disciplines involving wave propagation.
To simplify the notation, let = ˙ and define a collection of n 2 functions Φ j i by =. Theorem. (Douglas 1941) There exists a Lagrangian L : [0, T] × TM → R such that the equations (E) are its Euler–Lagrange equations if and only if there exists a non-singular symmetric matrix g with entries g ij depending on both u and v satisfying the following three Helmholtz conditions:
If one can evaluate the two integrals, one can find a solution to the differential equation. Observe that this process effectively allows us to treat the derivative as a fraction which can be separated. This allows us to solve separable differential equations more conveniently, as demonstrated in the example below.
In mathematics, the limiting amplitude principle is a concept from operator theory and scattering theory used for choosing a particular solution to the Helmholtz equation. The choice is made by considering a particular time-dependent problem of the forced oscillations due to the action of a periodic force.
The Sommerfeld radiation condition is used to solve uniquely the Helmholtz equation. For example, consider the problem of radiation due to a point source x 0 {\displaystyle x_{0}} in three dimensions, so the function f {\displaystyle f} in the Helmholtz equation is f ( x ) = δ ( x − x 0 ) , {\displaystyle f(x)=\delta (x-x_{0}),} where δ ...
The primary use of Green's functions in mathematics is to solve non-homogeneous boundary value problems. In modern theoretical physics , Green's functions are also usually used as propagators in Feynman diagrams ; the term Green's function is often further used for any correlation function .
The integral has the following form for a monochromatic wave: [2] [3] [4] = [^ ^],where the integration is performed over an arbitrary closed surface S enclosing the observation point , in is the wavenumber, in is the distance from an (infinitesimally small) integral surface element to the point , is the spatial part of the solution of the homogeneous scalar wave equation (i.e., (,) = as the ...