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<p dir="ltr">Hello,</p>
<p dir="ltr">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.<br>
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,</p>
<p dir="ltr">Andrea Testing,</p>
<p dir="ltr">Paul Scherrer Institut</p>
<p dir="ltr">Il 12/set/2016 08:50 PM, William Boyer <WBoyer@protoxrd.com> ha scritto:<br>
><br>
> 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.<br>
><br>
> <br>
><br>
> Best regards,<br>
><br>
> William Boyer<br>
><br>
> <br>
><br>
> From: gsas-ii-bounces@aps.anl.gov [mailto:gsas-ii-bounces@aps.anl.gov] On Behalf Of Toby, Brian H.<br>
> Sent: Monday, September 12, 2016 5:42 AM<br>
> To: Ivo Alxneit <ivo.alxneit@psi.ch><br>
> Cc: Von Dreele, Robert B. <vondreele@aps.anl.gov>; gsas-ii@mailman.aps.anl.gov<br>
> Subject: Re: [GSAS-II] Can Parameters be restricted?<br>
><br>
> <br>
><br>
> No. <br>
><br>
> <br>
><br>
> 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. <br>
><br>
> <br>
><br>
> Brian<br>
><br>
> <br>
>><br>
>> On Sep 12, 2016, at 10:27 AM, Ivo Alxneit <ivo.alxneit@psi.ch> wrote:<br>
>><br>
>> <br>
>><br>
>> Dear all<br>
>><br>
>> is there a way to restrict fitted parameters to a certain range? For<br>
>> example restrict site occupancies to positive numbers or to a range such<br>
>> as 0.9-1.0?<br>
>><br>
>> thanks for any help<br>
>> -- <br>
>> Dr. Ivo Alxneit<br>
>> Catalysis for Energy Group<br>
>> Bioenergy and Catalysis Laboratory phone: +41 56 310 4092<br>
>> Paul Scherrer Institute fax: +41 56 310 2688<br>
>> CH-5232 Villigen gnupg key: 0x515E30C7<br>
>> Switzerland<br>
>> https://www.psi.ch/ceg/catalysis-for-energy-group/<br>
>><br>
>> _______________________________________________<br>
>> GSAS-II mailing list<br>
>> GSAS-II@mailman.aps.anl.gov<br>
>> https://mailman.aps.anl.gov/mailman/listinfo/gsas-ii<br>
><br>
> <br>
><br>
> ********************************************************************<br>
><br>
> Brian H. Toby, Ph.D. office: 630-252-5488<br>
><br>
> Advanced Photon Source Chief Computational Scientist<br>
><br>
> Senior Physicist/Computational X-ray Science Group Leader<br>
><br>
> 9700 S. Cass Ave, Bldg. 401/B4192 cell: 630-327-8426 <br>
><br>
> Argonne National Laboratory <br>
><br>
> Argonne, IL 60439-4856 e-mail: brian dot toby at anl dot gov <br>
><br>
> ********************************************************************<br>
><br>
> "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."<br>
><br>
> <br>
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