code: public String getTextForExpression(DJGroup group, DJGroup childGroup, String type) {
  		return "new Double( $V{" + getReportName() + "_" +  getGroupVariableName(childGroup) + "}.doubleValue() / $V{" + getReportName() + "_" + getGroupVariableName(type,group.getColumnToGroupBy().getColumnProperty().getProperty()) + "}.doubleValue())";
  	}
docs: Returns the formula for the percentage
  @param group
  @param type
  @return