foreach my $j ($col_start .. $#column) {

    $n[$j] += 0; # add this to remove warning msg

    $x[$n[$j]][$j] = $column[$j];
    $x_tot[$j] += $x[$n[$j]][$j];
    $n[$j]++;
  }

##</code><code>##

my @n=0;
my @x_tot=0;
  my @g_jack_av=0;
  my @g_jack_err=0;

##</code><code>##

my @n;
my @x_tot;
  my @g_jack_av;
  my @g_jack_err;