I have not thought about if your constraint is a good idea, but I want to 
confirm that this type of constraint is not allowed within the current GUI.

The underlying constraint mechanism within GSAS-II would allow it to be 
included if input, but I am not sure how to write an interface that allows 
input and editing of completely general constraints.


On Oct 18, 2016, at 8:10 AM, Ivo Alxneit 
<ivo.alxn...@psi.ch<mailto:ivo.alxn...@psi.ch>> wrote:

Dear all

I have a series of X-ray powder diffractograms that show the segregation
of platinum from Pt4+ doped ceria. I would like to analyze the
segregation kinetics from these data.

I fit the Histogram Scale Factor and define a constrain that all phase
fractions add up to 1.0. For consistency I would like to set up a
constrain of the form

0:0:Scale * 0::Afrac:3 + 1:0:Scale

fraction_doped_ceria * Pt4+ occupancy plus fraction_segregated_platinum

i.e. a constrain that makes the amount of platinum in the system
constant (under the assumption that all platinum is 'visible' i.e. no
X-ray amorphous Pt clusters are present).

At present (Rev 2493) this does not seem to be possible and I try to
manually set the correct Pt4+ occupancy. This is rather tedious
iteration process. Could this be implemented in GSASII or is my analysis

Thanks for any suggestions
Dr. Ivo Alxneit
Catalysis for Energy Group
Bioenergy and Catalysis Laboratory        phone: +41 56 310 4092
Paul Scherrer Institute                     fax: +41 56 310 2688
CH-5232 Villigen                      gnupg key: 0x515E30C7

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