/***************************************************************************
 *
 * phase  -- fold light curve to a particular period and epoch.
 *
 * usage:
 *       phase period [epoch] < input  > output
 *
 * Examples:
 *       phase 1.28237982 <myfile
 *
 * Folds the lightcurve in myfile to a period of 1.28237982 days, 
 * streaming the data to stdout.  Since no explicit epoch was given,
 * it uses the JD of the first data point as the epoch.
 *
 *       phase 0.061042 1813.1234 <input.pho >output.pho
 *
 * Folds the light curve to a period of 0.061042 days, starting at
 * epoch 1813.1234 (same units as time in the input file).  Output 
 * is redirected to a second file as shown.
 *
 * Input Format:    
 *      hjd  magnitude  error
 *
 * Output Format:   
 *      hjd  phase  magnitude  error
 *
 * The epoch for folding the light curve is taken to be first input time
 * unless the epoch is given, in the same units as time appears in the
 * data files, is given as the second command-line argument.
 * 
 * based on phase.c by Donald Terndrup.
 *
 * Modified by R. Pogge, OSU Astronomy Dept.
 * pogge@astronomy.ohio-state.edu
 * 2000 Nov 10
 *
 ***************************************************************************/

#include <stdio.h>

main(argc,argv)
     int argc;
     char *argv[];
{

  double period;
  double jd, jd0, floor(), temp;
  float mag, toterr, phase;
  float n;
  double epoch;

  /* parse the command line */

  if (argc == 2) {
    sscanf(*++argv, "%lf", &period);
  } else if (argc == 3) {
    sscanf(*++argv, "%lf", &period);
    sscanf(*++argv, "%lf", &epoch);
    jd0 = -1.0;
  } else {
    printf("Usage: phase period [epoch] < input > output\n");
    exit(1);
  }

/* -- do the stuff -- */
	
  n = 0;

  while (scanf ("%lf %f %f", &jd, &mag, &toterr) != EOF) {
    if (n == 0) {
      if (jd0 == -1.0) 
	jd0 = epoch;
      else 
	jd0 = jd;
      printf("Using period %10.6lf days, epoch %10.6lf\n", period,jd0); 
    }

    temp  = (jd - jd0) / period;
    phase = (temp - floor(temp));
    
    printf ("%13.6f %12.8f %8.3f %8.3f\n", jd, phase, mag, toterr);

    n++; 
  }

}