如何用php在Jpgraph中设置虚线

require_once ('jpgraph/jpgraph.php');
require_once ('jpgraph/jpgraph_line.php');

$graph = new Graph(400, 300);

$graph->SetScale('textlin');
$graph->SetMargin(50, 30, 30, 50);

$lineplot = new LinePlot($data);

$lineplot->SetColor('blue');
$lineplot->SetWeight(2);

$lineplot->SetLineStyle('dashed');

$graph->Add($lineplot);

$graph->Stroke();