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