iPhone Chart: How can we zoom in in Core Plot ? (example code: AAPLot)

iPhone Chart: How can we zoom in in Core Plot ? (example code: AAPLot)

I am now using Core Plot to draw a Chart by example Code AAPLot

CPTGraphHostingView *graphHost;
IBOutlet UIScrollView *_scrollview;
IBOut开发者_StackOverflow中文版let UIView *zoom_view;    
APYahooDataPuller *datapuller;
CPTXYGraph *graph;

How to let the View zoom in and zoom out?