Hello, I would add that in case chemical analysis define a specific composition, constraint a compositional window in a certain moment of the refinement, would help to adjust other parameters more efficiently. Then, the constraint might be removed. Anyway, non-negative values or the possibility to let the parameters confined in a window is, in my view, not complicated to implement and very useful in several refinemens,
Andrea Testing, Paul Scherrer Institut Il 12/set/2016 08:50 PM, William Boyer <wbo...@protoxrd.com> ha scritto: > > 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> 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 >> 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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