HELP · SEE_ALSO

## NAME

yfit -- Compute Y-deflection calibration coefficients.

## USAGE

`yfit cctabin ypostab cctabout`

## DESCRIPTION

Using a table of Y-deflections as a function of carrousel position and spectral order, this task will determine the coefficients giving the Y-deflection by using a least squares fit, described as follows:

ydef = a + (b * w) + (c * w * w) + (d * m * w) where: w - is the wavelength computed with the carrousel calibration stored in 'cctabin', m - is the spectral order, a, b, c and d - are fitted coefficients. (d is not used for first order gratings (i.e., it is set to 0.0) and c is not used for Echelle modes.

## PARAMETERS

- cctabin [file name]
- Name of the input carrousel calibration table that is to be updated.
The carrousel coefficients
`CAP_A`,`CAP_B`, and`CAP_C`are copied directly from the input table to the output table. The Y-deflection coefficients`LIT_A`,`LIT_B`,`LIT_C`, and`LIT_D`are updated by this task. If`cctabin`has multiple rows, the first row in which the grating mode matches that of`ypostab`will be used.

- ypostab [file name]
- Name of the input Y-deflection table to be processed.
For first order grating
modes, table rows must be supplied for at least four carrousel positions.
For the Echelle mode, at least two carrousel positions, each having two spectral
orders, must be present in the table. This input table is the one generated by
the
`yfind`task.

- cctabout = "cctabout" [file name]
- Name for the output file that will contain the updated carrousel
calibration table produced by this task.
The
`cctabout`table will have one row containing the updated calibration of the selected row of`cctabin`.

## EXAMPLES

1. Compute the Y-deflection calibration for the input Y-position
table `ypostab.tab`. The table `oldcctab.tab` contains
the previous calibration and `newcctab.tab` will contain the updated
calibration.

hr> yfit oldcctab ypostab newcctab

## 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.