Re: [Gnuplot-info] Gnuplot "fit" command

[<ra...@be...>]

That solved the problem -- thanks for the help.

Before trying to use fit, I plotted the comma-seperated file and saw that
it came out OK. I assumed that this meant that gnuplot would understand
the data in its CSV form. I guess I was wrong.


- Jonathan

> Sorry, I meant:
>
> fit [1:15] f(x) "test.dat" via a
>
> or just
>
> fit f(x) "test.dat" via a
>
> Read "help data"!
>
> regards,
> Bernd
>
> ra...@be... schrieb:
>> Perhaps the mailing list does not allow attachements. I'll paste the
>> data
>> here:
>>
>> 1,0.4
>> 2,0.8
>> 3,1.2
>> 4,1.6
>> 5,2
>> 6,2.4
>> 7,2.8
>> 8,3.2
>> 9,3.6
>> 10,4
>> 11,4.4
>> 12,4.8
>> 13,5.2
>> 14,5.6
>> 15,6
>>
>>
>> It seems unlikely that playing with scaling factors should be necessary
>> as
>> this is the simplest data set possible and both variables are in the
>> same
>> order of magnitude. Thanks for the advice, though.
>>
>> - Jonathan
>>
>>
>>
>>
>>
>>> The attachment didn't make it.
>>> What is the range for x?
>>> If all number differ to much gnuplot will not find a good fit.
>>> You might have to play with scaling factors.
>>>
>>> Tammo
>>>
>>>
>>>
>>> On 5 Aug 2006 at 10:34, ra...@be... wrote:
>>>
>>>
>>>> I was looking for a good, simple program that will let me fit some
>>>> data
>>>> to
>>>> theoretical models. I decided to have a look at gnuplot and test it by
>>>> seeing if it can perform a simple linear fit. With the file attached
>>>> (testfile.csv), which fits y=0.4*x, I executed
>>>>
>>>> gnuplot> f(x) = a*x
>>>> gnuplot> fit f(x) "testfile.csv" via a
>>>>
>>>> I got the result
>>>>
>>>> Iteration 3
>>>> WSSR        : 4.13793           delta(WSSR)/WSSR   : -4.55122e-09
>>>> delta(WSSR) : -1.88326e-08      limit for stopping : 1e-05
>>>> lambda    : 0.00822598
>>>>
>>>> resultant parameter values
>>>>
>>>> a               = 1.10345
>>>>
>>>> After 3 iterations the fit converged.
>>>> final sum of squares of residuals : 4.13793
>>>> rel. change during last iteration : -4.55122e-09
>>>>
>>>> degrees of freedom (ndf) : 14
>>>> rms of residuals      (stdfit) = sqrt(WSSR/ndf)      : 0.54366
>>>> variance of residuals (reduced chisquare) = WSSR/ndf : 0.295567
>>>>
>>>> Final set of parameters            Asymptotic Standard Error
>>>> =======================            ==========================
>>>>
>>>> a               = 1.10345          +/- 0.01706      (1.546%)
>>>>
>>>>
>>>> correlation matrix of the fit parameters:
>>>>
>>>>                a
>>>> a               1.000
>>>>
>>>>
>>>>
>>>> Either I am missing something, or there is something very wrong with
>>>> gnuplot's fit command. The data should fit y=0.4*x exactly. I've tried
>>>> setting a to 0.43 before running the fit command and gotten the same
>>>> result.
>>>>
>>>> Any help?
>>>>
>>>> - Jonathan
>>>>
>>>
>>>
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