source: trunk/doc/expgui6.html @ 510

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# on 2001/12/19 18:55:42, toby did:
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1<html>
2<head>
3   <META NAME="Author" CONTENT="Brian H. Toby">
4   <title>EXPGUI</title>
5   <meta name="keywords" content="crystallography, Rietveld, diffraction,
6   GSAS, EXPGUI">
7</HEAD>
8<style>
9A:link {text-decoration:none}
10A:vlink {text-decoration:none}
11</style>
12
13<BODY BGCOLOR="#FFFFFF"
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15      text="#000000" link="#0033ff" vlink="#0033ff" alink="#0033ff">
16
17<?
18   include("/var/www/include/navigation.inc");
19   include("/var/www/include/utility.inc");
20?>
21<blockquote><font face="arial, helvetica, sans-serif">
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>
30<HR noshade width="75%" size="2" align="center">
31EXPGUI, part 6
32<HR noshade width="75%" size="2" align="center">
33</h1></center>
34
35<h3>A.6 Constraints pane</h3>
36<DL><DL>
37GSAS offers two types of restraints that can be included in a model.
38So called "soft constraints" or "restraints" penalize the fit if
39aspects of a model (for example, bond lengths) differ from selected values.
40So called "hard constraints" reduce the actual number of
41parameters in a model,
42by grouping parameters so that a single shift (possibly scaled) is
43applied to each parameter in the group.
44The constraints pane is used to set these "hard constraints."
45At this time the only constraints that can be set in EXPGUI are on atomic
46and profile profile (others can be set in EXPEDT).
47<P>
48Note that these constraints are only applied to shifts, but not to the
49actual values. This means that, for example,
50if two atoms
51are constrained so that the shift on their occupancy is the same, but
52the initial occupancies differ, the in occupancy difference will not change
53as the values refine.
54<P>
55Due to the way GSAS implements constraints, a parameter can be included
56in only one constraint. Should one or more parameters be constrained twice,
57the refinement results are unpredictable.
58
59</DL></DL>
60<a name="AtomConstraints"></a>
61<H4>Atom Constraints</H4>
62<DL><DL>
63The atom constraints editing pane appears below. Note that constraints can
64be listed sorted by constraint number, phase number, lowest atom number or
65variable by clicking on the buttons at the top of the pane.
66<P>
67To delete one or more constraints, click on the appropriate checkbuttons in the <B>Delete</B> column and the press the Delete button, below.
68</DL></DL>
69<img SRC="mc.gif" align=TEXTTOP  alt="EXPGUI Screen snapshot">
70<DL><DL>
71<a name="AtomConstraintsError"></a>
72Should parameters be included in more than one constraint,
73an error message is displayed, as shown below.
74Note that the constraint number is displayed as red on the main
75atomic constraints window (see above), if the
76constraint contains a parameter referenced elsewhere.
77Negative contraint values are highlighted with a beige background
78to make them more visible.
79
80</DL></DL>
81<img SRC="mcerr.gif" align=TEXTTOP  alt="EXPGUI Screen snapshot">
82<DL><DL>
83<a name="EditAtomConstraints"></a>
84<P>
85<img SRC="mcedit.gif" align=LEFT  alt="EXPGUI Screen snapshot">
86<img SRC="mcvar.gif" align=RIGHT alt="EXPGUI Screen snapshot">
87When the edit button for a constraint is pressed, the constraint is
88opened for editing. Controls are available to select the phase, variable,
89multiplier and atom(s). Note that for atom selection, use of the control key
90and the left mouse button allow individual atoms to be selected or deselected.
91Shift and the left mouse button allow ranges of atoms to be selected and the
92right mouse button selects all atoms
93<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
94<P>
95Note that it is inappropriate
96to constrain different types of parameters together, for example X and Uiso.
97The left-most variable button is the "master" which
98determines what variable are allowed in the
99other variable buttons.
100<P>
101When the "New Constraint" button is pressed, a blank constraint editing
102window is opened. Note that any variable to the right may then be selected,
103including three special codes, Uxx, XYZU and XYZU+-F.
104<UL><LI>
105XYZU creates
106four constraints,
107requiring the shifts on x, y, z and Uiso to be the same for all the selected
108atoms.
109<LI> 
110Uxx does the same for the six anisotropic displacement parameters.
111<LI>
112<a name="XYZUF"></a>XYZU+-F is used for pairs of atoms where
113the shifts on x, y, z and Uiso are required to be equal, but the shifts
114on Frac are opposite.
115</UL>
116These special codes are valuable for atoms that share a site or are
117otherwise grouped together.
118<P>
119<a name="AtomConstraintsMax"></a>
120Note that only 100 parameters may be included in a single atomic constraint,
121with one exception. When shifts for Uiso
122are constrained to the same value for all atoms in a phase,
123this counts as a single parameter. If more than 100
124parameters are entered for a constraint, an error message is shown.
125Up to 2000 total atomic constraints may be entered.
126EXPGUI does not warn if you exceed this limit.
127</DL></DL>
128
129<a name="ProfileConstraints"></a>
130<H4>Profile Constraints</H4>
131<DL><DL>
132The profile constraints editing pane appears below. Profile constraints
133are used to relate the shifts applied to profile terms for different
134phase/histogram combinations. Profile terms are identified by number,
135so while EXPEDT allows one to constrain the first profile term for
136a TOF histogram to a the first term in a CW histogram, EXPGUI attempts to
137make this impossible.
138<P>
139To delete one or more constraints, click on the appropriate checkbuttons
140in the <B>Delete</B> column and the press the Delete button, below.
141</DL></DL>
142<img SRC="pc.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
143<DL><DL>
144
145<a name="ProfileConstraintErr"></a>
146<img SRC="pcerr.gif" align=LEFT alt="EXPGUI Screen snapshot">
147Should parameters be included in more than one constraint,
148an error message is displayed, as shown below.
149Note that the constraint number is displayed as red on the main
150profile constraints window (see above), if the
151constraint contains a parameter referenced elsewhere.
152
153<BR CLEAR=LEFT>
154<P>
155<a name="EditProfileConstraints"></a>
156When the edit button for a constraint is pressed, the constraint is
157opened for editing, as shown below.
158Listboxes contain the available phases and histograms.
159Only the histograms of the same data type (TOF, CW or ED) are included,
160but no check is made to ensure that the
161selected phase/histogram combinations
162all have the same profile type.
163Note that for phase and histogram selection, use of the control key
164and the left mouse button allow individual items to be selected or deselected.
165Shift and the left mouse button allow ranges of items to be selected and the
166right mouse button selects all phases or histograms.
167<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
168<P>
169<img SRC="pcedit.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
170<P>
171</DL></DL>
172<a name="NewProfileConstraints"></a>
173<img SRC="pcnew1.gif" align=LEFT alt="EXPGUI Screen snapshot">
174When the "New Constraint" button is pressed, a window is opened to select
175the histogram and profile function type to be constrained. Note that
176only for profile function #4, where the number of terms depends on the
177phase symmetry, does it matter what phase you select. The available profile
178terms are displayed on the bottom of the window and more than
179one can be selected.
180<BR CLEAR=LEFT>
181<P>
182<DL><DL>
183<img SRC="pcnew2.gif" align=LEFT alt="EXPGUI Screen snapshot">
184
185After the "Continue" button is pressed, a constraint
186edit window is opened, as shown to the left.
187Listboxes contain the available phases and histograms and
188only the histograms of the selected data type are included, as before.
189Also, for phase and histogram selection, use of the control or shift key
190and the left mouse button allow individual items to be selected or deselected
191and the right mouse button selects all phases or histograms.
192Note that if more than one profile term was selected on the previous window,
193the same set of constraints are for each term.
194<BR CLEAR=LEFT>
195<P>
196<a name="ProfileConstraintsMax"></a>
197Note that only 27 terms can be included in a single profile constraint.
198Also, only like profile terms can be constrained. While GSAS does allow
199different types of profile terms to be constrained together, this does not
200usually make sense and EXPGUI does not allow it.
201</DL></DL>
202<hr>
203<TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT>
204<TR><TH><A  Href="expgui.html">EXPGUI top</A> 
205</TH><TH><A Href="expgui7.html">Next page</A>
206</TH><TH><A Href="expgui5.html">Previous page</A>
207</TH></TR></TABLE>
208
209<a href="http://www.ncnr.nist.gov/staff/toby/">Brian Toby</a> (<a href="mailto:brian.toby@nist.gov">Brian.Toby@NIST.GOV</a>)
210<br>
211$Revision: 510 $ $Date: 2009-12-04 23:07:22 +0000 (Fri, 04 Dec 2009) $
212</blockquote>
213</body>
214</html>
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