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

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 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

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On Feb 28, 2014, at 7:52 AM, Cristina Alonso Escobar 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

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,

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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 -----

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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

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