# Description of the program: polyback

This program performs a backward elimination for a given polynomial. This means it reads the terms of a polynomial from a parameter file (e.g. created by polypar) and removes term by term down to a given final number of remaining terms. The terms are removed in such a way that the onestep forecast error is increases minimally.

## Usage:

polyback [Options]

Everything not being a valid option will be interpreted as a potential datafile name. Given no datafile at all, means read stdin. Also - means stdin

Possible options are:

Option | Description | Default
--- | --- | ---
-l# | number of data to use | whole file
-x# | number of lines to be ignored | 0
-c# | column to be read | 1
-m# | embedding dimension | 2
-d# | delay | 1
-n# | length for the insample error estimation | all
-s# | steps to be forecasted | 1
-## | reduce down to # terms | 1
-p# | name of the input parameter file | parameter.pol
-o# | output file name (for the forecast errors); without -o data is written to stdout | 'datafile'.pbe
-V# | verbosity level 0: only panic messages 1: add input/output messages | 1
-h | show these options | none

## Description of the Output:

It creates a lot of new parameter files. For each term removed there is one file which is called parameter_input_file_name.n, where n is the number of remaining terms in the polynomial.
stdout or datafile.pbe contains the following information:
first column: number of remaining terms in the polynomial
second column: insample error produced by this polynomial
third column: out of sample error produced by this polynomial
fourth column: the term removed last from the polynomial

View the C-sources.

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