code: public void addColumn(float[] left, float[] right) {
          ColumnDef nextDef = new ColumnDef(left, right);
          if (!nextDef.isSimple()) simple = false;
          columnDefs.add(nextDef);
      }
docs: Add a new column.  The parameters are limits for each column
  wall in the format of a sequence of points (x1,y1,x2,y2,...).
  
  @param left  limits for left column
  @param right limits for right column