## GSLIB Help Page: BACKTR

Description:

- Back transform normal scores values according to a table look up

Parameters:

- datafl: a data file in simplified Geo-EAS format containing the normal scores.
- ivr: the column number for the normal scores.
- tmin and tmax: all values strictly less than tmin and strictly greater than tmax are ignored.
- outfl: the output file containing the back transformed values.
- transfl: an input file containing the transformation look-up table, i.e., pairs of z and y values with z being the original data values or class bound values and y being the corresponding normal scores values. This is an input file that corresponds to the table written out by `nscore`, `sgsim`,
- zmin and zmax: are the minimum and maximum values to be used for extrapolation in the tails.
- ltail and ltpar specify the back transformation implementation in the lower tail of the distribution: ltail=1 implements linear interpolation to the lower limit zmin and ltail=2 implements power model interpolation, with w=ltpar to the lower limit zmin
- Linear interpolation is used between known data values.
- utail and utpar specify the back transformation implementation in the upper tail of the distribution: utail=1 implements linear interpolation to the upper limit zmax utail=2 power model interpolation, with w=utpar to the upper limit zmax and utail=4 implements hyperbolic model extrapolation to the upper limit zmax with w = utpar