| Top: 80 observations of the double mode Cepheid TU Cas. Bottom: result of a PDM2 analysis of the primary variation period.
The PDM technique is a very fast and accurate method of determining periodic components of data sets with erratic time intervals, poor coverage, non-sine-wave curve shape, and/or large noise components. This is the type of data often encountered in the real world (especially in astronomical data), and in this case traditional Fourier methods are cumbersome and may yield misleading results.
The method was first derived in Stellingwerf, Astrophysical Journal, v224, p953, 1978. It is widely used. It has now been included as an application in the Stran language interpreter, including a new version (PDM2) with improved curve fits, suppressed subharmonics, and beta function statistics. For Unix systems, the source code for the PDM2 function is available here.
See also: Wikipedia article.