source: trunk/doc/expgui6.html @ 274

Last change on this file since 274 was 247, checked in by toby, 11 years ago

# on 2000/07/28 20:20:03, toby did:
document profile constraints

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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
38and profile profile (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>
47Due to the way GSAS implements constraints, a parameter can be included
48in only one constraint. Should one or more parameters be constrained twice,
49the refinement results are unpredictable.
50
51</DL></DL>
52<H4>Atom Constraints</H4>
53<DL><DL>
54The atom constraints editing pane appears below. Note that constraints can
55be listed sorted by constraint number, phase number, lowest atom number or
56variable by clicking on the buttons at the top of the pane.
57<P>
58To delete one or more constraints, click on the appropriate checkbuttons in the <B>Delete</B> column and the press the Delete button, below.
59</DL></DL>
60<img SRC="mc.gif" align=TEXTTOP>
61<DL><DL>
62
63Should parameters be included in more than one constraint,
64an error message is displayed, as shown below.
65Note that the constraint number is displayed as red on the main
66atomic constraints window (see above), if the
67constraint contains a parameter referenced elsewhere.
68
69</DL></DL>
70<img SRC="mcerr.gif" align=TEXTTOP>
71<DL><DL>
72<P>
73<img SRC="mcedit.gif" align=LEFT>
74<img SRC="mcvar.gif" align=RIGHT>
75When the edit button for a constraint is pressed, the constraint is
76opened for editing. Controls are available to select the phase, variable,
77multiplier and atom(s). Note that for atom selection, use of the control key
78and the left mouse button allow individual atoms to be selected or deselected.
79Shift and the left mouse button allow ranges of atoms to be selected and the
80right mouse button selects all atoms
81<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
82<P>
83Note that it is inappropriate
84to constrain different types of parameters together, for example X and Uiso.
85The left-most variable button is the "master" which
86determines what variable are allowed in the
87other variable buttons.
88<P>
89When the "New Constraint" button is pressed, a blank constraint editing
90window is opened. Note that any variable to the right may then be selected,
91including two special codes, Uxx and XYZU. XYZU creates four constraints,
92requiring the shifts on x, y, z and Uiso to be the same for all the selected
93atoms. Uxx does the same for the six anisotropic displacement parameters.
94These special codes are valuable for atoms that share a site.
95<P>
96Note that only 100 parameters may be included in a constraint,
97with one exception. When shifts for Uiso for all atoms in a phase
98are constrained, this counts as a single parameter. If more than 100
99parameters are entered for a constraint, an error message is shown.
100Up to 2000 atomic constraints may be entered.
101EXPGUI does not warn if you exceed this limit.
102</DL></DL>
103
104<H4>Profile Constraints</H4>
105<DL><DL>
106The profile constraints editing pane appears below. Profile constraints
107are used to relate the shifts applied to profile terms for different
108phase/histogram combinations. Profile terms are identified by number,
109so while EXPEDT allows one to constrain the first profile term for
110a TOF histogram to a the first term in a CW histogram, EXPGUI attempts to
111make this impossible.
112<P>
113To delete one or more constraints, click on the appropriate checkbuttons
114in the <B>Delete</B> column and the press the Delete button, below.
115</DL></DL>
116<img SRC="pc.gif" align=TEXTTOP>
117<DL><DL>
118
119<img SRC="pcerr.gif" align=LEFT>
120Should parameters be included in more than one constraint,
121an error message is displayed, as shown below.
122Note that the constraint number is displayed as red on the main
123profile constraints window (see above), if the
124constraint contains a parameter referenced elsewhere.
125
126<BR CLEAR=LEFT>
127<P>
128When the edit button for a constraint is pressed, the constraint is
129opened for editing, as shown below.
130Listboxes contain the available phases and histograms.
131Only the histograms of the same data type (TOF, CW or ED) are included,
132but no check is made to ensure that the
133selected phase/histogram combinations
134all have the same profile type.
135Note that for phase and histogram selection, use of the control key
136and the left mouse button allow individual items to be selected or deselected.
137Shift and the left mouse button allow ranges of items to be selected and the
138right mouse button selects all phases or histograms.
139<A href="expgui.html#mouseactions">(see Mouse Actions)</A>.
140<P>
141<img SRC="pcedit.gif" align=TEXTTOP>
142<P>
143</DL></DL>
144<img SRC="pcnew1.gif" align=LEFT>
145When the "New Constraint" button is pressed, a window is opened to select
146the histogram and profile function type to be constrained. Note that
147only for profile function #4, where the number of terms depends on the
148phase symmetry, does it matter what phase you select. The available profile
149terms are displayed on the bottom of the window and more than
150one can be selected.
151<BR CLEAR=LEFT>
152<P>
153<DL><DL>
154<img SRC="pcnew2.gif" align=LEFT>
155
156After the "Continue" button is pressed, a constraint
157edit window is opened, as shown to the left.
158Listboxes contain the available phases and histograms and
159only the histograms of the selected data type are included, as before.
160Also, for phase and histogram selection, use of the control or shift key
161and the left mouse button allow individual items to be selected or deselected
162and the right mouse button selects all phases or histograms.
163Note that if more than one profile term was selected on the previous window,
164the same set of constraints are for each term.
165
166<BR CLEAR=LEFT>
167</DL></DL>
168<hr>
169<A Href="expgui.html">EXPGUI top</A>
170
171<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>)
172<br>
173$Revision: 247 $ $Date: 2009-12-04 23:02:51 +0000 (Fri, 04 Dec 2009) $
174</body>
175</html>
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