title: Subtracting two dates with perl DateTime
body: <p>I try to subtract two dates from each other but unfortunately without success. Maybe someone could give me a hand. My first try looks like:</p>
  
  <pre><code>
  #!/usr/bin/perl -w
  #use strict;
  use warnings;
  use DateTime;
  
  $today = DateTime->now( time_zone => 'Europe/Berlin' );
  $today = $today->ymd;
  
  my $year = '2011';
  my $month = '03';
  my $day = '22';
  
  my $dt1 = DateTime-> new (
                       year => $year,
                       month => $month,
                       day   => $day,
                       time_zone =>'Europe/Berlin'
                       );
  
  my $mydate = $dt1->ymd;
  
  my $sub = $today->subtract_datetime($mydate);
  
  print "subtraction: $sub \n";
  </code></pre>
  
  <p>Thanks in advance.</p>