source: trunk/doc/expgui6.html @ 336

Last change on this file since 336 was 336, checked in by toby, 12 years ago

# on 2000/10/18 00:11:17, toby did:
fixup formatting

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  • Property rcs:rev set to 1.6
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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>
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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<br clear=all><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<a name="AtomConstraints"></a>
59<H4>Atom Constraints</H4>
60<DL><DL>
61The atom constraints editing pane appears below. Note that constraints can
62be listed sorted by constraint number, phase number, lowest atom number or
63variable by clicking on the buttons at the top of the pane.
64<P>
65To delete one or more constraints, click on the appropriate checkbuttons in the <B>Delete</B> column and the press the Delete button, below.
66</DL></DL>
67<img SRC="mc.gif" align=TEXTTOP  alt="EXPGUI Screen snapshot">
68<DL><DL>
69<a name="AtomConstraintsError"></a>
70Should parameters be included in more than one constraint,
71an error message is displayed, as shown below.
72Note that the constraint number is displayed as red on the main
73atomic constraints window (see above), if the
74constraint contains a parameter referenced elsewhere.
75
76</DL></DL>
77<img SRC="mcerr.gif" align=TEXTTOP  alt="EXPGUI Screen snapshot">
78<DL><DL>
79<a name="EditAtomConstraints"></a>
80<P>
81<img SRC="mcedit.gif" align=LEFT  alt="EXPGUI Screen snapshot">
82<img SRC="mcvar.gif" align=RIGHT alt="EXPGUI Screen snapshot">
83When the edit button for a constraint is pressed, the constraint is
84opened for editing. Controls are available to select the phase, variable,
85multiplier and atom(s). Note that for atom selection, use of the control key
86and the left mouse button allow individual atoms to be selected or deselected.
87Shift and the left mouse button allow ranges of atoms to be selected and the
88right mouse button selects all atoms
89<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
90<P>
91Note that it is inappropriate
92to constrain different types of parameters together, for example X and Uiso.
93The left-most variable button is the "master" which
94determines what variable are allowed in the
95other variable buttons.
96<P>
97When the "New Constraint" button is pressed, a blank constraint editing
98window is opened. Note that any variable to the right may then be selected,
99including two special codes, Uxx and XYZU. XYZU creates four constraints,
100requiring the shifts on x, y, z and Uiso to be the same for all the selected
101atoms. Uxx does the same for the six anisotropic displacement parameters.
102These special codes are valuable for atoms that share a site.
103<P>
104<a name="AtomConstraintsMax"></a>
105Note that only 100 parameters may be included in a single atomic constraint,
106with one exception. When shifts for Uiso
107are constrained to the same value for all atoms in a phase,
108this counts as a single parameter. If more than 100
109parameters are entered for a constraint, an error message is shown.
110Up to 2000 total atomic constraints may be entered.
111EXPGUI does not warn if you exceed this limit.
112</DL></DL>
113
114<a name="ProfileConstraints"></a>
115<H4>Profile Constraints</H4>
116<DL><DL>
117The profile constraints editing pane appears below. Profile constraints
118are used to relate the shifts applied to profile terms for different
119phase/histogram combinations. Profile terms are identified by number,
120so while EXPEDT allows one to constrain the first profile term for
121a TOF histogram to a the first term in a CW histogram, EXPGUI attempts to
122make this impossible.
123<P>
124To delete one or more constraints, click on the appropriate checkbuttons
125in the <B>Delete</B> column and the press the Delete button, below.
126</DL></DL>
127<img SRC="pc.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
128<DL><DL>
129
130<a name="ProfileConstraintErr"></a>
131<img SRC="pcerr.gif" align=LEFT alt="EXPGUI Screen snapshot">
132Should parameters be included in more than one constraint,
133an error message is displayed, as shown below.
134Note that the constraint number is displayed as red on the main
135profile constraints window (see above), if the
136constraint contains a parameter referenced elsewhere.
137
138<BR CLEAR=LEFT>
139<P>
140<a name="EditProfileConstraints"></a>
141When the edit button for a constraint is pressed, the constraint is
142opened for editing, as shown below.
143Listboxes contain the available phases and histograms.
144Only the histograms of the same data type (TOF, CW or ED) are included,
145but no check is made to ensure that the
146selected phase/histogram combinations
147all have the same profile type.
148Note that for phase and histogram selection, use of the control key
149and the left mouse button allow individual items to be selected or deselected.
150Shift and the left mouse button allow ranges of items to be selected and the
151right mouse button selects all phases or histograms.
152<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
153<P>
154<img SRC="pcedit.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
155<P>
156</DL></DL>
157<a name="NewProfileConstraints"></a>
158<img SRC="pcnew1.gif" align=LEFT alt="EXPGUI Screen snapshot">
159When the "New Constraint" button is pressed, a window is opened to select
160the histogram and profile function type to be constrained. Note that
161only for profile function #4, where the number of terms depends on the
162phase symmetry, does it matter what phase you select. The available profile
163terms are displayed on the bottom of the window and more than
164one can be selected.
165<BR CLEAR=LEFT>
166<P>
167<DL><DL>
168<img SRC="pcnew2.gif" align=LEFT alt="EXPGUI Screen snapshot">
169
170After the "Continue" button is pressed, a constraint
171edit window is opened, as shown to the left.
172Listboxes contain the available phases and histograms and
173only the histograms of the selected data type are included, as before.
174Also, for phase and histogram selection, use of the control or shift key
175and the left mouse button allow individual items to be selected or deselected
176and the right mouse button selects all phases or histograms.
177Note that if more than one profile term was selected on the previous window,
178the same set of constraints are for each term.
179<BR CLEAR=LEFT>
180<P>
181<a name="ProfileConstraintsMax"></a>
182Note that only 27 terms can be included in a single profile constraint.
183Also, only like profile terms can be constrained. While GSAS does allow
184different types of profile terms to be constrained together, this does not
185usually make sense and EXPGUI does not allow it.
186</DL></DL>
187<hr>
188<TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT>
189<TR><TH><A  Href="expgui.html">EXPGUI top</A> 
190</TH><TH><A Href="expgui7.html">Next page</A>
191</TH><TH><A Href="expgui5.html">Previous page</A>
192</TH></TR></TABLE>
193
194<a href="http://www.ncnr.nist.gov/staff/toby/">Brian Toby</a> (<a href="mailto:brian.toby@nist.gov">Brian.Toby@NIST.GOV</a>)
195<br>
196$Revision: 336 $ $Date: 2009-12-04 23:04:21 +0000 (Fri, 04 Dec 2009) $
197</body>
198</html>
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