[GSAS-II] constain combining Scale and Afrac

[Ivo Alxneit]

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
faulted?

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
Switzerland
https://www.psi.ch/ceg/catalysis-for-energy-group/

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