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## NAME

deadtimey -- Compute FOS paired-pulse coefficients.

## USAGE

`deadtimey observed expected table pptab`

## DESCRIPTION

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

y = x / (1 + tx) where: y - is the observed count rate, x - is the true count rate, t - is a 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. q0 and q1 are determined as follows: 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 selectable user values. 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 vectors of observed count rates. The maximum total number of data points in all input files is 50,000.

- expected [file name template]
- File names of the vectors of expected count rates corresponding
to the file names specified in
`observed`.

- table = "deadtimey" [file name]
- Output table of fit results. 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 "fos" (char*3). 'DETECTOR' - Detector number (1 for amber, 2 for blue) (integer). 'TAU1' - Set to 0.0 (real). 'EPSILON' - Set to 0.0 (real). 'THRESHOLD' - Set to value of 'threshold' parameter (double). 'Q0' - First paired-pulse coefficient (double). 'Q1' - Second paired-pulse coefficient (double) 'F' - Set to the value of the 'f' parameter (double). 'ITERATIONS' - Set to 1 (integer).

- (f = 50000.0) [real]
- Threshold above which the linear function for the time coefficient is to be used.

- (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= 70000.0) [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.

- (detector = "both") [string, allowed values: amber | blue | both]
- Detector name for which this calibration is to be used.
If set to "both", the output table,
`pptab`, will have two rows (one per detector), otherwise,`pptab`will have one row corresponding to the specified detector.

- (eps = 0.1) [real]
- The RSDP error allowed in paired-pulse correction (this is not used
in
`deadtimey`).

- (iter = 10.0) [real]
- The number of iterations in RSDP (this is not used in
`deadtimey`).

## EXAMPLES

1. Compute the paired-pulse coefficients using the data files
`obs` and `exp`.

hr> deadtimey obs exp fittab pptab

Now plot the computed time coefficient (column `TIME` in `fittab`) as a
function of the
observed count rate (column `OBSERVED` in `fittab`). Examine the plot to
identify better choices for `c1`, `c2`, `c3`, `c4`, and `f`. For example,
the following adjustments might be made:

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

The `deadtimey` task can now be rerun with the new parameters.

hr> deadtimey

## BUGS

## REFERENCES

Howard Bushouse, STSDAS

## 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