Re: [Gnuplot-info] fiting exponential does not match

[Thomas S. <t.s...@fz...>]

your fit parameters are not independent:

'c', which is used to compensate an 'offset', depends on 'a',
because
a*exp(0) = a*1
which means that 'c+a' should be '116'.

you could set 'c' to 116, 'a' and 'b' to some reasonable
value (e.g. a=1, b=0.02) and fit 'via a,b', adjust 'c' and
fit again.


terriblement wrote:
> 
> Hi everybody,
> 
> I have a txt file with some values, and I want to fit a curve with my
> values...(see attached file)
> 
>  http://old.nabble.com/file/p32115817/test.txt test.txt 
> 
> it looks like an exponential function, so I'Ve tried this :
> 
> f(x) = a* exp (b*x) + c
> c = 116
> fit f(x) "test.txt" using 1:2 via a,b,c
> 
> and the values are totally wrong :s
> I don't understand what I'm doing wrong, if somebody could help me (I'm
> noob with gnuplot)
> 
> thanks a lot.
> 

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