FindFit

FindFit[data,expr,pars,vars] finds numerical values of the parameters pars that make expr give a best fit to data as a function of vars. 

FindFit[data,{expr,cons},pars,vars] finds a best fit subject to the parameter constraints cons.

FindFit[data,exprspec,pars,vars,"prop"]  specifies what fit property prop should be returned.

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