[Ifeffit] Fwd: problems with setting parameters in new Artemis (Demeter 0.9.16)

[Chris Patridge]

I wanted to add that you need a reasonable measure of confidence that these are the only  paths contributing because otherwise you could receive negative values for a or b in the fit results if there are other paths involved by using this simple constraint. 

Chris 

********************************************
Dr. Christopher Patridge
Assistant Professor of Chemistry
Math and Natural Science Dept
BFAC 009
D'Youville College
320 Porter Ave., Buffalo, NY 14150
716-829-8096

Sent from my iPhone

> On Feb 28, 2014, at 8:04 AM, Chris Patridge <patridge at buffalo.edu> wrote:
> 
> Hi,
> 
> The easiest constraint would be a mathematical expression such as "a + b = 1". Do you have an experimental value for so2 as found for something chemically similar such as a standard at that edge?  Then replace so2 expression for each path as "value found * a" and "value found * b".  This should give a relative percentage for each path contribution. 
> 
> Hope that is clear,
> 
> Chris
> 
> ********************************************
> Dr. Christopher Patridge
> Assistant Professor of Chemistry
> Math and Natural Science Dept
> BFAC 009
> D'Youville College
> 320 Porter Ave., Buffalo, NY 14150
> 716-829-8096
> 
> Sent from my iPhone
> 
>> On Feb 28, 2014, at 7:52 AM, Cristina Alonso Escobar <criales at itq.upv.es> wrote:
>> 
>> Dear All,
>> 
>> I am trying to fit the first FT shell in Artemis with a mixture of two different compounds (octahedral and tetrahedral models). I would like to quantify the ratio between this two compounds in my sample so I decided to multiply So2 by a parameter called "a" in one model and by "(1-a)" in the other.
>> 
>> I would like to know:
>> 
>> 1.- How can I restrain "a" ? I tried to  manually add a restraint, but I do not know how to make an interval restraint...( 0<a<1)
>> 
>> 2.- If you select "restrain" and after in the math expression "build restrain from ..."
>> What is the meaning of scale by?
>> Why the program duplicate the restrain (i.e restrain- a and restrain- res_a - 1* penalty (a, 0, 1)?
>> I think I am not doing well because the value of my parameter "a" is suspiciously always 0.
>> 
>> 
>> 
>> Thank you in advance,
>> 
>> 
>> 
>> *** *** *** *** *** *** *** *** ***
>> 
>> Cristina Alonso-Escobar. PhD student
>> 
>> Instituto de Tecnología Química (UPV-CSIC)
>> Avda. de los Naranjos s/n
>> 46022 Valencia (Spain)
>> 
>> http://itq.upv-csic.es
>> 
>> Tfno: +34 96 387 7800
>> Fax:  +34 96 387 9444
>> 
>> ----- Terminar mensaje reenviado -----
>> 
>> 
>> *** *** *** *** *** *** *** *** ***
>> 
>> Cristina Alonso-Escobar. PhD student
>> 
>> Instituto de Tecnología Química (UPV-CSIC)
>> Avda. de los Naranjos s/n
>> 46022 Valencia (Spain)
>> 
>> http://itq.upv-csic.es
>> 
>> Tfno: +34 96 387 7800
>> Fax:  +34 96 387 9444
>> 
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
> 
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit