#!/usr/bin/perl -w

#
# t_distribution
# Copyright (C) 2006 by John Heidemann <johnh@isi.edu>
# $Id: t_distribution,v 1.1 2006/08/25 05:11:38 johnh Exp $
#
# This program is distributed under terms of the GNU general
# public license, version 2.  See the file COPYING
# in $dblibdir for details.
#
sub usage {
    print <<END;
usage: $0 [-c conf_pct] sample_count

Show the T-distribution value for a given confidence interval percentage
and number of samples.

Used mostly for debugging.

Options:

    -c CONF    specific confidence interval percentage (defaults to 0.95)

Sample input:
(nothing)

Sample command:
t_distribution

Sample output:
xxx
END
    exit 1;
}

# require 5.000;

BEGIN {
    $dblibdir = "/home/johnh/BIN/DB";
    push(@INC, $dblibdir);
}
require "$dblibdir/dblib.pl";
use DbGetopt;
use DbTDistr;

my(@orig_argv) = @ARGV;
my($prog) = &progname;
my $conf_pct = 0.95;
my($dbopts) = new DbGetopt("c:?", \@ARGV);
while ($dbopts->getopt) {
    $ch = $dbopts->opt;
    if ($ch eq 'c') {
	$conf_pct = $dbopts->optarg;
    } else {
	&usage;
    };
};
&usage if ($#ARGV != 0);
my($n) = $ARGV[0];


# no standard jdb header or trailer
my $alpha = 1.0 - $conf_pct;
my $conf_alpha = (1.0 - $conf_pct) / 2.0;
my $t = &DbTDistr::t_distribution($n - 1, $conf_alpha);

printf "confidence_percent: %s\nn: %d\nalpha: %f\ndf: %d\nt(alpha,df): %.6f\n", $conf_pct, $n, $alpha, $n-1, $t;

exit 0;