[Ifeffit] Fitting parameters corrleations between variables

[pushkar shejwalkar]

Dear Matt,
  Thank you very much for your response. One more question. What value of
corelation is acceptable/publishable? also having a correlation number
means the fit is not finished and I should change the values of variable
that are correlated? is that so?
Best
Pushkar

On Tue, Nov 24, 2015 at 1:48 PM, Matt Newville <newville at cars.uchicago.edu>
wrote:

> Pushkar,
>
> On Mon, Nov 23, 2015 at 8:59 PM, pushkar shejwalkar <
> pshejwalkar2004 at gmail.com> wrote:
>
>> Dear All,
>>     I am trying to fit in Pd compound and the fit that I obtained looks
>> kinda good. I used Pd metal and Pd(OAc)2 shells for fitting. These
>> standards were collected and fitted simultaneously and I got the SO2 value
>> there as 0.67 with Pd foil coordination number as 12 which is correct when
>> considered Pd foil CN. Next while fitting the actual sample (unknown) I
>> used the formula in SO2 column as amp*N1 and put amp as 0.67 and N as 1. I
>> kept N1 as variable (Guess). same I did for the second shell of Pd-O with
>> N2. amp is kept on SET value of 0.67. After fitting I received the N1 and
>> N2 value as 5.6 (0.5) and 1.6 (0.7) (roughly). however, when I checked the
>> correlations between the variables I got the values as given in the log
>> file attached. I saw there is some correlation between bkg01_01 and N2 and
>> many such correlations between bkg values. I have so far never seen such
>> correlations. What are the implications of these correlations? does this
>> means that my fitting assumptions are incorrect. does correlations values
>> in negative indicates something?
>>
>
> Correlation between two variables A and B means that if you changed one
> variable (A) away from its best-fit value, you could improve that fit by
> changing the other variable (B).  In fact the correlation tells you by how
> much, and (from the sign) in what direction that change would be.
>
> A correlation of 0 means that if one changed A, B would not need to change
> at all. A correlation of 1 would mean that a change in A by 1 standard
> error (the reported error), B would have to change by 1 standard error.
> And, again, the sign gives the direction of that change.
>
> Having correlated values does not mean that your assumptions are incorrect.
>
> Thank you very much for the input. By the way my RBKG is 1.2 in athena and
>> I used this same file for fitting purpose and on artemis I used rmin 1.2
>> and rmax 3.4. All these information are in log file attached
>> Any help in understanding this is appreciated.
>>
>> --
>> Best Regards,
>> Pushkar Shejwalkar.
>> Post-doctoral -Researcher,
>> Tokyo Engineering University,
>> Tokyo-to
>> Japan
>>
>>
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>
> --Matt
>
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-- 
Best Regards,
Pushkar Shejwalkar.
Post-doctoral -Researcher,
Tokyo Engineering University,
Tokyo-to
Japan
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