Perturbation theory is a large collection of iterative methods for obtaining approximate solutions to problems involving a small parameter ε. These methods are so powerful that sometimes it is actually advisable to introduce a parameter e temporarily into a difficult problem having no small parameter, and then finally to set ε = 1 to recover the original problem. This apparently artificial conversion to a perturbation problem may be the only way to make progress.
KeywordsBranch Point Perturbation Method Perturbation Series Singular Perturbation Problem Matched Asymptotic Expansion
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