sub check_list {
   my $r = shift;
   my ($min, $max) = minmax(@$r);
   my $ctr_lin = ($min+$max)/2;
   my $ctr_log = (log($min)+log($max))/2;
   my ($cnt_lin, $cnt_log)=(0,0);
   for (@$r) {
      ++$cnt_lin if $_ < $ctr_lin;
      ++$cnt_log if $_ < $ctr_log;
   }
   my $error_lin = abs($ctr_lin - @$r/2);
   my $error_log = abs($ctr_log - @$r/2);
   return $error_lin < $error_log ? "linear" : "log";
}