2,2,2,2.0001
2,2,2,1

##</code><code>##

my $c0 = 20001.9999999578;    # as computed by gsl_fit_linear()
my $c1 = -9999.9999999789;
say $c0 + $c1 * $_ for 2, 2.0001;

__END__
2
1