source: trunk/doc/expgui6.html @ 356

Last change on this file since 356 was 356, checked in by toby, 14 years ago

# on 2000/11/27 21:10:45, toby did:
define XYZU+-F
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  • Property rcs:date set to 2000/11/27 21:10:45
  • Property rcs:lines set to +15 -4
  • Property rcs:rev set to 1.8
  • Property rcs:state set to Exp
  • Property svn:keywords set to Author Date Revision Id
File size: 8.6 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"
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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.
75Negative contraint values are highlighted with a beige background
76to make them more visible.
77
78</DL></DL>
79<img SRC="mcerr.gif" align=TEXTTOP  alt="EXPGUI Screen snapshot">
80<DL><DL>
81<a name="EditAtomConstraints"></a>
82<P>
83<img SRC="mcedit.gif" align=LEFT  alt="EXPGUI Screen snapshot">
84<img SRC="mcvar.gif" align=RIGHT alt="EXPGUI Screen snapshot">
85When the edit button for a constraint is pressed, the constraint is
86opened for editing. Controls are available to select the phase, variable,
87multiplier and atom(s). Note that for atom selection, use of the control key
88and the left mouse button allow individual atoms to be selected or deselected.
89Shift and the left mouse button allow ranges of atoms to be selected and the
90right mouse button selects all atoms
91<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
92<P>
93Note that it is inappropriate
94to constrain different types of parameters together, for example X and Uiso.
95The left-most variable button is the "master" which
96determines what variable are allowed in the
97other variable buttons.
98<P>
99When the "New Constraint" button is pressed, a blank constraint editing
100window is opened. Note that any variable to the right may then be selected,
101including three special codes, Uxx, XYZU and XYZU+-F.
102<UL><LI>
103XYZU creates
104four constraints,
105requiring the shifts on x, y, z and Uiso to be the same for all the selected
106atoms.
107<LI> 
108Uxx does the same for the six anisotropic displacement parameters.
109<LI>
110<a name="XYZUF"></a>XYZU+-F is used for pairs of atoms where
111the shifts on x, y, z and Uiso are required to be equal, but the shifts
112on Frac are opposite.
113</UL>
114These special codes are valuable for atoms that share a site or are
115otherwise grouped together.
116<P>
117<a name="AtomConstraintsMax"></a>
118Note that only 100 parameters may be included in a single atomic constraint,
119with one exception. When shifts for Uiso
120are constrained to the same value for all atoms in a phase,
121this counts as a single parameter. If more than 100
122parameters are entered for a constraint, an error message is shown.
123Up to 2000 total atomic constraints may be entered.
124EXPGUI does not warn if you exceed this limit.
125</DL></DL>
126
127<a name="ProfileConstraints"></a>
128<H4>Profile Constraints</H4>
129<DL><DL>
130The profile constraints editing pane appears below. Profile constraints
131are used to relate the shifts applied to profile terms for different
132phase/histogram combinations. Profile terms are identified by number,
133so while EXPEDT allows one to constrain the first profile term for
134a TOF histogram to a the first term in a CW histogram, EXPGUI attempts to
135make this impossible.
136<P>
137To delete one or more constraints, click on the appropriate checkbuttons
138in the <B>Delete</B> column and the press the Delete button, below.
139</DL></DL>
140<img SRC="pc.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
141<DL><DL>
142
143<a name="ProfileConstraintErr"></a>
144<img SRC="pcerr.gif" align=LEFT alt="EXPGUI Screen snapshot">
145Should parameters be included in more than one constraint,
146an error message is displayed, as shown below.
147Note that the constraint number is displayed as red on the main
148profile constraints window (see above), if the
149constraint contains a parameter referenced elsewhere.
150
151<BR CLEAR=LEFT>
152<P>
153<a name="EditProfileConstraints"></a>
154When the edit button for a constraint is pressed, the constraint is
155opened for editing, as shown below.
156Listboxes contain the available phases and histograms.
157Only the histograms of the same data type (TOF, CW or ED) are included,
158but no check is made to ensure that the
159selected phase/histogram combinations
160all have the same profile type.
161Note that for phase and histogram selection, use of the control key
162and the left mouse button allow individual items to be selected or deselected.
163Shift and the left mouse button allow ranges of items to be selected and the
164right mouse button selects all phases or histograms.
165<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
166<P>
167<img SRC="pcedit.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
168<P>
169</DL></DL>
170<a name="NewProfileConstraints"></a>
171<img SRC="pcnew1.gif" align=LEFT alt="EXPGUI Screen snapshot">
172When the "New Constraint" button is pressed, a window is opened to select
173the histogram and profile function type to be constrained. Note that
174only for profile function #4, where the number of terms depends on the
175phase symmetry, does it matter what phase you select. The available profile
176terms are displayed on the bottom of the window and more than
177one can be selected.
178<BR CLEAR=LEFT>
179<P>
180<DL><DL>
181<img SRC="pcnew2.gif" align=LEFT alt="EXPGUI Screen snapshot">
182
183After the "Continue" button is pressed, a constraint
184edit window is opened, as shown to the left.
185Listboxes contain the available phases and histograms and
186only the histograms of the selected data type are included, as before.
187Also, for phase and histogram selection, use of the control or shift key
188and the left mouse button allow individual items to be selected or deselected
189and the right mouse button selects all phases or histograms.
190Note that if more than one profile term was selected on the previous window,
191the same set of constraints are for each term.
192<BR CLEAR=LEFT>
193<P>
194<a name="ProfileConstraintsMax"></a>
195Note that only 27 terms can be included in a single profile constraint.
196Also, only like profile terms can be constrained. While GSAS does allow
197different types of profile terms to be constrained together, this does not
198usually make sense and EXPGUI does not allow it.
199</DL></DL>
200<hr>
201<TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT>
202<TR><TH><A  Href="expgui.html">EXPGUI top</A> 
203</TH><TH><A Href="expgui7.html">Next page</A>
204</TH><TH><A Href="expgui5.html">Previous page</A>
205</TH></TR></TABLE>
206
207<a href="http://www.ncnr.nist.gov/staff/toby/">Brian Toby</a> (<a href="mailto:brian.toby@nist.gov">Brian.Toby@NIST.GOV</a>)
208<br>
209$Revision: 356 $ $Date: 2009-12-04 23:04:45 +0000 (Fri, 04 Dec 2009) $
210</body>
211</html>
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