If your data is noisy, limits can also help keep the parameters from getting stuck in physically impossible local minima. For example, I might set a minimum FWHM to a little less than the narrowest peak my instrument can produce, then a few random points that happen to be above average cannot be mistaken for a peak.
Best regards, William Boyer From: gsas-ii-boun...@aps.anl.gov [mailto:gsas-ii-boun...@aps.anl.gov] On Behalf Of Toby, Brian H. Sent: Monday, September 12, 2016 5:42 AM To: Ivo Alxneit <ivo.alxn...@psi.ch> Cc: Von Dreele, Robert B. <vondre...@aps.anl.gov>; gsas-ii@mailman.aps.anl.gov Subject: Re: [GSAS-II] Can Parameters be restricted? No. To be honest I am not sure why one would want to do this. When a parameter refines "out of range” it tells you something about your data or model. With a restraint, you would never know that for example, a Uiso value is refining negative by > 2 sigma or a occupancy is >>1. It makes sense to me to define a model so that the sum of occupancies is fixed — a well defined assumption. Defining a range for a parameter scares me as I could never know that my model is highly flawed is some way. Brian On Sep 12, 2016, at 10:27 AM, Ivo Alxneit <ivo.alxn...@psi.ch <mailto:ivo.alxn...@psi.ch> > wrote: Dear all is there a way to restrict fitted parameters to a certain range? For example restrict site occupancies to positive numbers or to a range such as 0.9-1.0? thanks for any help -- 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/ _______________________________________________ GSAS-II mailing list GSAS-II@mailman.aps.anl.gov <mailto:GSAS-II@mailman.aps.anl.gov> https://mailman.aps.anl.gov/mailman/listinfo/gsas-ii ******************************************************************** Brian H. Toby, Ph.D. office: 630-252-5488 Advanced Photon Source Chief Computational Scientist Senior Physicist/Computational X-ray Science Group Leader 9700 S. Cass Ave, Bldg. 401/B4192 cell: 630-327-8426 Argonne National Laboratory Argonne, IL 60439-4856 e-mail: brian dot toby at anl dot gov ******************************************************************** "We will restore science to its rightful place, and wield technology's wonders... We will harness the sun and the winds and the soil to fuel our cars and run our factories... All this we can do. All this we will do."
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