function resize_koppel(num,columns) {
    var max_height = 0;   
     for(var i = 0; i <= (num/columns); i++) {
      for(var j = 1; j <= columns; j++) {
       var column_no = (i*columns)+j;
         if(column_no <= num){
           var koppel = document.getElementById("koppelbox"+column_no).offsetHeight;
           if(koppel > max_height){
             max_height = koppel;
           }  
        }           
      }
      for(var j = 1; j <= columns; j++) {
        var column_no = (i*columns)+j;
        if(column_no <= num){
            document.getElementById("koppelbox"+column_no).style.height = max_height;     
        }          
      }
      max_height = 0;
    }
}