NonlinearModelFit

NonlinearModelFit[{{x1,y1},{x2,y2},…},form,{β1,…},x] constructs a nonlinear model with formula form that fits the yi for each xi using the free parameters βi.

NonlinearModelFit[data,form,params,{x1,…}] constructs a nonlinear model where form depends on the variables xk. 

NonlinearModelFit[data,{form,cons},params,{x1,…}] constructs a nonlinear model subject to the parameter constraints cons.

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