source: trunk/doc/expgui6.html @ 299

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# on 2000/10/03 23:28:06, toby did:
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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<TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT>
24<TR><TH><A  Href="expgui.html">EXPGUI top</A> 
25</TH><TH><A Href="expgui7.html">Next page</A>
26</TH><TH><A Href="expgui5.html">Previous page</A>
27</TH></TR></TABLE><BR CLEAR=ALL>
28
29<center><h1>
30EXPGUI, part 6
31</h1></center>
32
33<h3>A.6 Constraints pane</h3>
34<DL><DL>
35GSAS offers two types of restraints that can be included in a model.
36So called "soft constraints" or "restraints" penalize the fit if
37aspects of a model (for example, bond lengths) differ from selected values.
38So called "hard constraints" reduce the actual number of
39parameters in a model,
40by grouping parameters so that a single shift (possibly scaled) is
41applied to each parameter in the group.
42The constraints pane is used to set these "hard constraints."
43At this time the only constraints that can be set in EXPGUI are on atomic
44and profile profile (others can be set in EXPEDT).
45<P>
46Note that these constraints are only applied to shifts, but not to the
47actual values. This means that, for example,
48if two atoms
49are constrained so that the shift on their occupancy is the same, but
50the initial occupancies differ, the in occupancy difference will not change
51as the values refine.
52<P>
53Due to the way GSAS implements constraints, a parameter can be included
54in only one constraint. Should one or more parameters be constrained twice,
55the refinement results are unpredictable.
56
57</DL></DL>
58<H4>Atom Constraints</H4>
59<DL><DL>
60The atom constraints editing pane appears below. Note that constraints can
61be listed sorted by constraint number, phase number, lowest atom number or
62variable by clicking on the buttons at the top of the pane.
63<P>
64To delete one or more constraints, click on the appropriate checkbuttons in the <B>Delete</B> column and the press the Delete button, below.
65</DL></DL>
66<img SRC="mc.gif" align=TEXTTOP  alt="EXPGUI Screen snapshot">
67<DL><DL>
68
69Should parameters be included in more than one constraint,
70an error message is displayed, as shown below.
71Note that the constraint number is displayed as red on the main
72atomic constraints window (see above), if the
73constraint contains a parameter referenced elsewhere.
74
75</DL></DL>
76<img SRC="mcerr.gif" align=TEXTTOP  alt="EXPGUI Screen snapshot">
77<DL><DL>
78<P>
79<img SRC="mcedit.gif" align=LEFT  alt="EXPGUI Screen snapshot">
80<img SRC="mcvar.gif" align=RIGHT alt="EXPGUI Screen snapshot">
81When the edit button for a constraint is pressed, the constraint is
82opened for editing. Controls are available to select the phase, variable,
83multiplier and atom(s). Note that for atom selection, use of the control key
84and the left mouse button allow individual atoms to be selected or deselected.
85Shift and the left mouse button allow ranges of atoms to be selected and the
86right mouse button selects all atoms
87<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
88<P>
89Note that it is inappropriate
90to constrain different types of parameters together, for example X and Uiso.
91The left-most variable button is the "master" which
92determines what variable are allowed in the
93other variable buttons.
94<P>
95When the "New Constraint" button is pressed, a blank constraint editing
96window is opened. Note that any variable to the right may then be selected,
97including two special codes, Uxx and XYZU. XYZU creates four constraints,
98requiring the shifts on x, y, z and Uiso to be the same for all the selected
99atoms. Uxx does the same for the six anisotropic displacement parameters.
100These special codes are valuable for atoms that share a site.
101<P>
102Note that only 100 parameters may be included in a constraint,
103with one exception. When shifts for Uiso for all atoms in a phase
104are constrained, this counts as a single parameter. If more than 100
105parameters are entered for a constraint, an error message is shown.
106Up to 2000 atomic constraints may be entered.
107EXPGUI does not warn if you exceed this limit.
108</DL></DL>
109
110<H4>Profile Constraints</H4>
111<DL><DL>
112The profile constraints editing pane appears below. Profile constraints
113are used to relate the shifts applied to profile terms for different
114phase/histogram combinations. Profile terms are identified by number,
115so while EXPEDT allows one to constrain the first profile term for
116a TOF histogram to a the first term in a CW histogram, EXPGUI attempts to
117make this impossible.
118<P>
119To delete one or more constraints, click on the appropriate checkbuttons
120in the <B>Delete</B> column and the press the Delete button, below.
121</DL></DL>
122<img SRC="pc.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
123<DL><DL>
124
125<img SRC="pcerr.gif" align=LEFT alt="EXPGUI Screen snapshot">
126Should parameters be included in more than one constraint,
127an error message is displayed, as shown below.
128Note that the constraint number is displayed as red on the main
129profile constraints window (see above), if the
130constraint contains a parameter referenced elsewhere.
131
132<BR CLEAR=LEFT>
133<P>
134When the edit button for a constraint is pressed, the constraint is
135opened for editing, as shown below.
136Listboxes contain the available phases and histograms.
137Only the histograms of the same data type (TOF, CW or ED) are included,
138but no check is made to ensure that the
139selected phase/histogram combinations
140all have the same profile type.
141Note that for phase and histogram selection, use of the control key
142and the left mouse button allow individual items to be selected or deselected.
143Shift and the left mouse button allow ranges of items to be selected and the
144right mouse button selects all phases or histograms.
145<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
146<P>
147<img SRC="pcedit.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
148<P>
149</DL></DL>
150<img SRC="pcnew1.gif" align=LEFT alt="EXPGUI Screen snapshot">
151When the "New Constraint" button is pressed, a window is opened to select
152the histogram and profile function type to be constrained. Note that
153only for profile function #4, where the number of terms depends on the
154phase symmetry, does it matter what phase you select. The available profile
155terms are displayed on the bottom of the window and more than
156one can be selected.
157<BR CLEAR=LEFT>
158<P>
159<DL><DL>
160<img SRC="pcnew2.gif" align=LEFT alt="EXPGUI Screen snapshot">
161
162After the "Continue" button is pressed, a constraint
163edit window is opened, as shown to the left.
164Listboxes contain the available phases and histograms and
165only the histograms of the selected data type are included, as before.
166Also, for phase and histogram selection, use of the control or shift key
167and the left mouse button allow individual items to be selected or deselected
168and the right mouse button selects all phases or histograms.
169Note that if more than one profile term was selected on the previous window,
170the same set of constraints are for each term.
171
172<BR CLEAR=LEFT>
173</DL></DL>
174<hr>
175<TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT>
176<TR><TH><A  Href="expgui.html">EXPGUI top</A> 
177</TH><TH><A Href="expgui7.html">Next page</A>
178</TH><TH><A Href="expgui5.html">Previous page</A>
179</TH></TR></TABLE>
180
181<a href="http://www.ncnr.nist.gov/staff/toby/">Brian Toby</a> (<a href="mailto:brian.toby@nist.gov">Brian.Toby@NIST.GOV</a>)
182<br>
183$Revision: 297 $ $Date: 2009-12-04 23:03:42 +0000 (Fri, 04 Dec 2009) $
184</body>
185</html>
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