Lib for nonlinear editing on iOS

I need to set some data in an iOS app, mainly with Newton Law of Cooling:

y = a + b * c^{x}

      

        
        
        
      

    

I found that the GNU Scientific Library can handle this, however it does not count for the GPL. Is there an open source Chi-Square open source algorithm in C / C ++ with a commercially friendly license (e.g. BSD, APL, etc.)?

We are looking forward to your offer.