NAME

odeadtimez -- Compute the GHRS paired-pulse coefficients.

USAGE

odeadtimez observed expected table pptab

DESCRIPTION

This routines computes the diode paired pulse coefficients for the following equation:

	y = x / (1 + tx)
 
where:
	y - observed count rate,
	x - true count rate, and
	t - time constant which is a piece-wise linear
		function of Y.
		If y <= f then t = q0,
		if y > f then t = q0 + q1 * (y - f),
		where 'f' is an input parameter.

The parameters 'q0' and 'q1' are determined by the following method:
 
1) For each pair of observed, x(i), and expected, y(i), count rates,
   the effective time coefficient, t(i), is computed by:

       t(i) = (x(i) - y(i)) / (x(i) * y(i))

2) The values of t(i) where c1 < y(i) < c2, are averaged to
   give 'q0'.  'c1' and 'c2' are set by the user.

3) A linear least squares fit is done for pairs of y(i) and t(i)
   for points where c3 < y(i) < c4.  'c3' and 'c4' are user selectable
   parameters.  The fit gives coefficients 'q1' to the linear equation
   passing through the point (f,q0).

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 to the the images in observed.

table = "odeadtimez" [file name]

Output table for the fit results produced by odeadtimez. This table will have the following columns:

     'OBSERVED'     - Observed count rates (real).
     'EXPECTED'     - Expected count rates (real).
     'TIME'         - Computed time coefficient for each data 
		      point (real).
     'TIME_FIT'     - Fitted time coefficient for the observed 
		      count rate (real).
     'EXPECTED_FIT' - Fitted expected count rates for the
		      observed count rates (real).

pptab = "pptab" [file name]

Name of the output paired-pulse table for use by the Routine Science Data Processing (RSDP) system. This table will contain the following columns (the columns TAU1, EPSILON, and ITERATIONS are not used by this task):

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

(f = 50000.0) [real]

Threshold above which to use the linear function for the time coefficient.

(c= 30000.0) [real, min=0.0, max=100000.0]

Lower limit of the count rate range for computing q0.

(c= 40000.0) [real, min=0.0, max=100000.0]

Upper limit of the count rate range for computing q0.

(c= 50000.0) [real, min=0.0, max=100000.0]

Lower limit of the count rate range for computing q1.

(c= 60000.0) [real, min=0.0, max=100000.0]

Upper limit of the count rate range for computing q1.

(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 to the output table.

(eps = 0.1) [real]

Allowed error in the paired-pulse correction---used by RSDP.

(iter = 10.0) [real]

Number of iterations allowed in RSDP.

(detector=0) [integer, min=0, max=2]

Detector number being used for this calibration. If set to "0" (for both detectors), the pptab output table will have two rows (one per detector). Otherwise, 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> odeadtimez obs exp fittab pptab

Now plot the computed time coefficient (the TIME column in the table fittab) as a function of the observed count rate (the OBSERVED column in fittab). Examine the plot to identify better choices for c1, c2, c3, c4, and f. Make any necessary adjustments, for example, the following two commands define new values for the c2 and f parameters.

	hr> odeadtimez.c2 = 45000.
 	hr> odeadtimez.f = 48000.

Now rerun odeadtimez with the new parameters.

	hr> odeadtimez

BUGS

REFERENCES

HELP

For assistance using this or any other tasks, please contact help@stsci.edu or call the help desk at 410-338-1082.

SEE ALSO