how to restrict scrolling for +ve part in cpxygraph

I am new to core plot SDK, implemented core plot in my app. i need to restrict -v开发者_C百科e part of graph. i.e always i will have +ve values for graph((1,1),(10,15),(20,15)).i need horizontal , vertical scrolling for +ve part only.So i want to restrict remaining 3 parts of graph. I tried in all ways help less, so posted here. if any one already done with this type requirement, please help me ASAP.

Thanks in advance.

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The easiest way to restrict the scrolling ranges is to set the globalXRange and globalYRange properties on your plot space. If you want more control, you can use a plot space delegate. CPTestApp (the Mac version) demonstrates both techniques.