Perturbation theory

Methods of mathematical approximation

In mathematics, perturbation theory comprises methods for finding an approximate solution to a problem, by starting from the exact solution of a related, simpler problem. A critical feature of the technique is a middle step that breaks the problem into "solvable" and "perturbative" parts. In regular perturbation theory, the solution is expressed as a power series in a small parameter ε {\displaystyle \varepsilon } .

From Wikipedia, under CC BY-SA. More on occurri.