This is more of an objective C question that a ShinobiCharts question as ShinobiCharts is a subclass of UIView, and will lay itself out in the CGRect you provide for its frame. If you want to have your chart to be at the top of your view, and take up 1/3 of the screen (vertically?) then I would do the following:
ShinobiChart *myChart = [[ShinobiChart alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height/3)];
Or if your chart is already initialised:
myChart.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height/3);
As for plotting functions, this isn't currently possible directly. If you wanted to plot a function you would need to calculate the points in the fuction yourself and then plot them on your chart!
I am glad you like our trial keys , you could always put it in a property list if it gets a bit annoying bang in the middle of your code .