NAME: pdmshif PURPOSE: (one line) Zero-point shift search by phase dispersion minimization ($\theta$ based). DESCRIPTION: This routine computes the Theta statistic to look for the optimum zero-point shift between two datasets for a given period. The theta statistic is the same as used for period searching in time-series data using the technique described by Stellingwerf, ApJ, 224, pp. 953-960 (1978). The shift reported is that which is added to x2 to register with respect to x1. CATEGORY: Photometry CALLING SEQUENCE: pdmshif,t1,x1,sig1,t2,x2,sig2,period,shif1,shif2,dshif,shiftv,theta INPUTS: t1 - independent variable for first dataset (usually time) x1 - dependent variable for first dataset (usually magnitude or intensity) sig1 - Uncertainty on x for first dataset. t2 - independent variable for first dataset (usually time) x2 - dependent variable for first dataset (usually magnitude or intensity) sig2 - Uncertainty on x for first dataset. period - Lightcurve period. (same units as t1 and t2). shif1 - Lower limit to zero-point shift (units=[x1]) shif2 - Upper limit to zero-point shift (units=[x1]) dshif - Frequency interval. (units=[1/t]) OPTIONAL INPUT PARAMETERS: KEYWORD PARAMETERS: OUTPUTS: shiftv - Zero-point shift vector. theta - PDM statistic (1 ==> insignificant, 0 ==> significant). COMMON BLOCKS: SIDE EFFECTS: RESTRICTIONS: PROCEDURE: MODIFICATION HISTORY: Written 1992 Feb 13, by Marc W. Buie, Lowell Observatory 95/02/23 - MWB - added NBINS keyword