deadtimez

deadtimez

stsdas.hst_calib.hrs.z_calib

deadtimez

NAME · USAGE · DESCRIPTION · PARAMETERS: · EXAMPLES · BUGS
REFERENCES · HELP · SEE_ALSO

NAME

deadtimez -- Compute GHRS paired pulse coefficients.

USAGE

deadtimez observed expected table pptab

DESCRIPTION

This routines computes the paired pulse, or deadtime coefficient, for the equation:

	y = (1 - exp(-tx)) / t
 
where:
	y - observed count rate,
	x - true count rate, and
	t - time coefficient.

The value of "t" is computed using a least squares fit to an input set of observed count rates, x, versus expected count rates, y. The Levenberg-Marquardt iterative method is used to compute the least squares value of t by minimizing chi-squared.

PARAMETERS:

observed [file name template]: File names of the images of observed count rates. The maximum total number of data points in all input images is 50,000.

expected [file name template]: File names of the images of expected count rates corresponding the the observed count rates in observed.

table = "deadtimez" [file name]

Output table of fit results. This table will have the following columns:

     'EXPECTED' - Expected count rates (real).
     'OBSERVED' - Observed count rates (real).
     'OBS_FIT'  - Fitted values of the observed count rates (real).
     'RESIDUAL' - Residuals of the fit (real).

pptab = "pptab" [file name]

Name of the output paired pulse table created by deadtimez (for use by the Routine Science Data Processing (RSDP) system). (Table columns EPSILON, Q0, Q1, F, and ITERATIVE are not used by the deadtimez task.) The table has the following columns:

     'INSTRUMENT' - Set to "HRS" (character*3).
     'DETECTOR'   - Detector number (1 or 2) (integer).
     'TAU1'       - Set to the computed time coefficient (double).
     'EPSILON'    - Set to "0.0" (real).
     'THRESHOLD'  - Set to the value of the 'threshold' input 
		    parameter (double).
     'Q0'         - Set to "0.0" (real).
     'Q1'         - Set to "0.0" (real).
     'F'          - Set to "0.0" (real).
     'ITERATIONS' - Set to "1"  (integer).

(tau= 10.2e-6) [real]: Initial guess for the time coefficient.

(niter = 10) [integer]: Number of iterations of the Levenberg-Marquardt least squares method.

(threshold = 1.0) [real]: Value of the threshold used by RSDP to decide if a correction to the input observed count rate is needed. This parameter is simply copied from the input table to the output table.

(detector=0) [integer, min=0, max=2]: Detector number for which this calibration is to be used. If set to "0" (for both detectors), the output table, pptab, will have two rows (one per detector). Otherwise, the output table, pptab, will have one row corresponding to the specified detector.

EXAMPLES

1. Compute the paired pulse coefficients using the data images obs and exp.

	cl> deadtimez obs exp fittab pptab