source: trunk/doc/expgui6.html @ 223

Last change on this file since 223 was 223, checked in by toby, 11 years ago

# on 2000/07/03 21:41:08, toby did:
Constraints pane

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  • Property rcs:date set to 2000/07/03 21:41:08
  • Property rcs:rev set to 1.1
  • Property rcs:state set to Exp
  • Property svn:keywords set to Author Date Revision Id
File size: 4.2 KB
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1<html>
2<head>
3   <META NAME="Author" CONTENT="Brian H. Toby">
4   <title>EXPGUI</title>
5</head>
6<BODY BGCOLOR="#FFFFFF">
7
8<A HREF=http://www.ncnr.nist.gov>
9<IMG SRC="http://www.ncnr.nist.gov/images/ncnrtrans.gif" 
10alt="Link to NIST Center for Neutron Research home page"
11ALIGN=RIGHT></A>
12<A HREF=http://www.nist.gov>
13<IMG SRC="http://www.ncnr.nist.gov/images/webidblue_2lineright.gif" 
14alt="Link to National Institute of Standards & Technology home page"
15ALIGN=LEFT></A>
16<CENTER>
17<A Href="http://www.ncnr.nist.gov/programs/crystallography/software/tclpkgs.html">
18<IMG SRC="tcltklogo100.gif" 
19alt="Link to Tcl/Tk information">
20</CENTER></A>
21<hr>
22
23<center><h1>
24EXPGUI
25</h1></center>
26<A Href="expgui.html">EXPGUI top</A>
27<h3>A.6 Constraints pane</h3>
28<DL><DL>
29GSAS offers two types of restraints that can be included in a model.
30So called "soft constraints" or "restraints" penalize the fit if
31aspects of a model (for example, bond lengths) differ from selected values.
32So called "hard constraints" reduce the actual number of
33parameters in a model,
34by grouping parameters so that a single shift (possibly scaled) is
35applied to each parameter in the group.
36The constraints pane is used to set these "hard constraints."
37At this time the only constraints that can be set in EXPGUI are on atomic
38parameters (others can be set in EXPEDT).
39<P>
40Note that these constraints are only applied to shifts but not to the
41actual values. This means that, for example,
42if two atoms
43are constrained so that the shift on their occupancy is the same, but
44the initial occupancies differ, the in occupancy difference will not change
45as the values refine.
46<P>
47<H4>Atom Constraints</H4>
48The atom constraints editing pane appears below. Note that constraints can
49be listed sorted by constraint number, phase number, lowest atom number or
50variable by clicking on the buttons at the top of the pane.
51<P>
52To delete one or more constraints, click on the appropriate checkbuttons in the <B>Delete</B> column and the press the Delete button, below.
53</DL></DL>
54<img SRC="mc.gif" align=TEXTTOP>
55<DL><DL>
56
57Due to the way GSAS implements these constraints, a parameter can be included
58in only one constraint. Should one or more parameters be constrained twice,
59an error message is shown as shown below.
60Note that the constraint number is displayed as red, for constraints that
61have conflicts in the constraints editing pane (see above.)
62</DL></DL>
63<img SRC="mcerr.gif" align=TEXTTOP>
64<DL><DL>
65<P>
66<img SRC="mcedit.gif" align=LEFT>
67<img SRC="mcvar.gif" align=RIGHT>
68When the edit button for a constraint is pressed, the constraint is
69opened for editing. Controls are available to select the phase, variable,
70multiplier and atom(s). Note that for atom selection, use of the control key
71and the left mouse button allow individual atoms to be selected or deselected.
72Shift and the left mouse button allow ranges of atoms to be selected and the
73right mouse button selects all atoms
74<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
75<P>
76Note that it is inappropriate
77to constrain different types of parameters together, for example X and Uiso.
78The left-most variable button is the "master" which
79determines what variable are allowed in the
80other variable buttons.
81<P>
82When the "New Constraint" button is pressed, a blank constraint editing
83window is opened. Note that any variable to the right may then be selected,
84including two special codes, Uxx and XYZU. XYZU creates four constraints,
85requiring the shifts on x, y, z and Uiso to be the same for all the selected
86atoms. Uxx does the same for the six anisotropic displacement parameters.
87These special codes are valuable for atoms that share a site.
88<P>
89Note that only 100 parameters may be included in a constraint,
90with one exception. When shifts for Uiso for all atoms in a phase
91are constrained, this counts as a single parameter. If more than 100
92parameters are entered for a constraint, an error message is shown.
93Up to 2000 atomic constraints may be entered.
94EXPGUI does not warn if you exceed this limit.
95</DL></DL>
96
97<hr>
98<A Href="expgui.html">EXPGUI top</A>
99
100<p><a href="http://www.ncnr.nist.gov/staff/toby/">Brian Toby</a> (<a href="mailto:brian.toby@nist.gov">Brian.Toby@NIST.GOV</a>)
101<br>
102$Revision: 223 $ $Date: 2009-12-04 23:02:27 +0000 (Fri, 04 Dec 2009) $
103</body>
104</html>
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