如何为这个系列设置辅助轴?
$series = new PHPExcel_Chart_DataSeries(
PHPExcel_Chart_DataSeries::TYPE_LINECHART, // plotType
PHPExcel_Chart_DataSeries::GROUPING_CLUSTERED, // plotGrouping
$chartOrder, // plotOrder
$chartLables, // plotLabel
$chartCategories, // plotCategory
$chartValues // plotValues
);
$series->setPlotDirection(PHPExcel_Chart_DataSeries::DIRECTION_COL);
$plotarea = new PHPExcel_Chart_PlotArea(null, array($series));
$legend = new PHPExcel_Chart_Legend(PHPExcel_Chart_Legend::POSITION_BOTTOM, null, false);
$chart = new PHPExcel_Chart(
"chart_$topRow_$leftColumn", // name
null, // title
$legend, // legend
$plotarea, // plotArea
true, // plotVisibleOnly
0, // displayBlanksAs
null, // xAxisLabel
null // yAxisLabel
);
$chart->setTopLeftPosition('A1');
$chart->setBottomRightPosition(K12');
$objWorksheet->addChart($chart);