multiple function curves in core-plot - objective-c

Question

I'm currently trying to add more than one mathematical function curves. Below is part of my code.
// draw all expression curves (in viewDidLoad)
for ( j=0; j<self.expNum; j++ ) {
[self getDataForPlot1:self.plotIndex]; // get DataForPlot of one selected expression
[self addCurve:self.plotIndex];
}
I'm trying to add all curves after drawing the axes, but it is only the last input curve that is drawn. How can I separate the dataForPlot for each function?
-(void)getDataForPlot1:(int)index
{
int i;
NSString *exp;
int bound, plotNum;
double interval;
bound = 3 * scaleX;
plotNum = 3 * 60;
interval = (double)bound / plotNum;
NSMutableArray *contentArray = [NSMutableArray arrayWithCapacity:2*plotNum];
for ( i = -plotNum; i < plotNum; i++ ) {
id x;
x = [NSNumber numberWithFloat: i * interval];
// get one expression
.......
id y = [exp numberByEvaluatingString]; // get y values from the expression
[contentArray addObject:[NSMutableDictionary dictionaryWithObjectsAndKeys:x, #"x", y, #"y", nil]];
}
dataForPlot = contentArray;
}
-(void)addCurve:(int)index {
CPTScatterPlot *boundLinePlot = [[CPTScatterPlot alloc] init];
CPTMutableLineStyle *lineStyle = [CPTMutableLineStyle lineStyle];
lineStyle.miterLimit = 1.0f;
lineStyle.lineWidth = 3.0f;
lineStyle.lineColor = [CPTColor blueColor];
boundLinePlot.dataLineStyle = lineStyle;
boundLinePlot.identifier = #"Blue Plot";
boundLinePlot.dataSource = self;
[graph addPlot:boundLinePlot toPlotSpace:plotSpace];
boundLinePlot.interpolation = CPTScatterPlotInterpolationCurved;
}

Answer 1

(Answering the question based on comments above)
Save a copy of each dataset separately. It looks like the calculated plot data gets overwritten each time you call -getDataForPlot1:.
Also, set a unique identifier for each plot so the datasource can know which one is requesting data.