NAME: pdm PURPOSE: (one line) Period search by phase dispersion minimization ($\theta$ based). DESCRIPTION: This routine computes the Theta statistic for period searching in time-series data using the technique described by Stellingwerf, ApJ, 224, pp. 953-960 (1978). CATEGORY: Photometry CALLING SEQUENCE: pdm,t,x,sigx0,freq1,freq2,dfreq,freq,period,theta INPUTS: t - independent variable (usually time) x0 - dependent variable (usually magnitude or intensity) sigx0 - Uncertainty on x. freq1 - Lower limit to frequency to compute statistic (units=[1/t]) freq2 - Upper limit to frequency to compute statistic (units=[1/t]) dfreq - Frequency interval. (units=[1/t]) OPTIONAL INPUT PARAMETERS: KEYWORD PARAMETERS: OUTPUTS: freq - Frequency vector. period - inverse frequency. theta - PDM statistic (1 ==> insignificant, 0 ==> significant). COMMON BLOCKS: SIDE EFFECTS: RESTRICTIONS: PROCEDURE: MODIFICATION HISTORY: Written 1992 Feb 11, by Marc W. Buie, Lowell Observatory