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Re: NonlinearFit problem


Feng-Yin Chang wrote:
> Hi All,
>    Could anyone give me any suggestion for the specified  fitting function
>    f= r^a Exp[-b r]?
>    My data point was given below,
>    data={{0, 1.00002}, {2.31507, 26.4522}, {4.32033, 56.8265}, {6.63539,
>     59.6674}, {8.64066, 39.5536}, {10.9557, 21.6862}, {12.961,
>     10.1456}, {15.276, 4.39652}}
> 
>   The following way,
>    NonlinearFit[data,f,r,{a,b}], gives the error message,
>    FindFit::njnum:
>    The Jacobian is not a matrix of numbers at (a,b)={1.,1.}.
> 
>   How should I do this fitting without the problem?
> 
> 
> Feng-Yin Chang,
> Institute of Physics,NCTU,Taiwan
> 

If you remove your first data point you get a fit. The first data point 
can't fit because the value of f[r] at r=0 can only be 0, infinity, or 
indeterminate. It would be nice if the statistics package gave a better 
diagnostic for what must be a common occurrence!

David Bailey


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