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  2. Perturbation theory - Wikipedia

    en.wikipedia.org/wiki/Perturbation_theory

    In mathematics and applied mathematics, perturbation theory comprises methods for finding an approximate solution to a problem, by starting from the exact solution of a related, simpler problem. [ 1 ] [ 2 ] A critical feature of the technique is a middle step that breaks the problem into "solvable" and "perturbative" parts. [ 3 ]

  3. Perturbation function - Wikipedia

    en.wikipedia.org/wiki/Perturbation_function

    In mathematical optimization, the perturbation function is any function which relates to primal and dual problems. The name comes from the fact that any such function defines a perturbation of the initial problem.

  4. Perturbation - Wikipedia

    en.wikipedia.org/wiki/Perturbation

    Perturbation or perturb may refer to: Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly; Perturbation (geology), changes in the nature of alluvial deposits over time; Perturbation (astronomy), alterations to an object's orbit (e.g., caused by gravitational interactions with other ...

  5. Perturbation theory (quantum mechanics) - Wikipedia

    en.wikipedia.org/wiki/Perturbation_theory...

    Perturbation theory is an important tool for describing real quantum systems, as it turns out to be very difficult to find exact solutions to the Schrödinger equation for Hamiltonians of even moderate complexity.

  6. Singular perturbation - Wikipedia

    en.wikipedia.org/wiki/Singular_perturbation

    Singular perturbation theory is a rich and ongoing area of exploration for mathematicians, physicists, and other researchers. The methods used to tackle problems in this field are many. The more basic of these include the method of matched asymptotic expansions and WKB approximation for spatial problems, and in time, the Poincaré–Lindstedt ...

  7. Feynman diagram - Wikipedia

    en.wikipedia.org/wiki/Feynman_diagram

    The number of times the interaction Hamiltonian acts is the order of the perturbation expansion, and the time-dependent perturbation theory for fields is known as the Dyson series. When the intermediate states at intermediate times are energy eigenstates (collections of particles with a definite momentum) the series is called old-fashioned ...

  8. Eigenvalue perturbation - Wikipedia

    en.wikipedia.org/wiki/Eigenvalue_perturbation

    In mathematics, an eigenvalue perturbation problem is that of finding the eigenvectors and eigenvalues of a system = that is perturbed from one with known eigenvectors and eigenvalues =. This is useful for studying how sensitive the original system's eigenvectors and eigenvalues x 0 i , λ 0 i , i = 1 , … n {\displaystyle x_{0i},\lambda _{0i ...

  9. Celestial mechanics - Wikipedia

    en.wikipedia.org/wiki/Celestial_mechanics

    Perturbation methods start with a simplified form of the original problem, which is carefully chosen to be exactly solvable. In celestial mechanics, this is usually a Keplerian ellipse , which is correct when there are only two gravitating bodies (say, the Earth and the Moon ), or a circular orbit, which is only correct in special cases of two ...