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1<html>
2<head>
3   <title>EXPGUI Alumina Tutorial, part #6</title>
4</head>
5
6<style>
7A:link {text-decoration:none}
8A:vlink {text-decoration:none}
9</style>
10
11<BODY BGCOLOR="#FFFFFF"
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14
15<?
16   include("/var/www/include/navigation.inc");
17   include("/var/www/include/utility.inc");
18?>
19<blockquote>
20
21<TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT>
22<TR><TH><A  Href="index.html">Intro</A> 
23</TH><TH><A Href="alumina7.html">Next page</A>
24</TH><TH><A Href="alumina5.html">Previous page</A>
25</TH></TR></TABLE><BR CLEAR=ALL>
26
27
28<CENTER>
29<H1><HR noshade width="75%" size="2" align="center">
30GSAS/EXPGUI Alumina tutorial (part 6)<BR>
31Plotting the Initial Fit
32<HR noshade width="75%" size="2" align="center">
33</H1>
34</CENTER>
35<I>While Chi-squared and R-values provide some measure of how a fit is
36progressing, the only way to actually understand the quality of the
37fit and what problems need to be corrected, is to look at agreement between
38the observed diffraction data and the corresponding values computed
39from the fit. This is sometimes called a Rietveld plot.</I>
40<P>
41The GSAS program POWPLOT and the EXPGUI program LIVEPLOT allow the
42fit to be examined graphically. In this tutorial step, LIVEPLOT is used
43to examine the results.
44<P><HR noshade width="50%" size="4" align="center"><P>
45Press the LIVEPLOT button on the button bar (or use a menu command) to
46start LIVEPLOT. You should then see a plot like the one below.
47<P><img alt="tutorial screen dump" src="6a.gif" align=RIGHT>
48<BR clear=all>
49<P><blockquote><I>
50In this plot, the data are "X" characters, the calculated values are
51a red line. The fitted background is shown as a green line. Offset below,
52the observed pattern minus the computed pattern is shown in blue.
53The observed and computed values do not agree very well, but seem to follow
54the same trends. In the subsequent plots we will see in more detail what
55some of the discrepancies are.
56<P>
57Note that the size of the plot can be changed by changing the size of the
58window.
59</I></blockquote>
60<P><HR noshade width="50%" size="4" align="center"><P>
61It will help to see the actual positions of the reflections. This display
62can be turned on by pressing the "1" key (1 for phase 1, 2 for phase 2...)
63in the LIVEPLOT window. (This can also be done using the Tickmarks
64submenu in the File menu.)
65<P><img alt="tutorial screen dump" src="6b.gif" align=RIGHT>
66<BR clear=all>
67<P><blockquote><I>
68Note that the color, length, style, placement of the tick mark lines can be
69changed in the Options menu.
70<P>
71Note also that the reflection indices for a tick mark can be
72displayed by pressing the "h" key when the cursor is positioned
73over a tick mark.
74</I></blockquote>
75<P><HR noshade width="50%" size="4" align="center"><P>
76
77With all the data displayed, at appears that the tick marks are in the
78right places at lower angles, but are not well placed at 140 degrees and
79higher. It would be good to see the plot at high magnification to see more
80detail, however. "Zooming in" is accomplished by clicking the mouse in the
81lower left and upper right corners of the region to be viewed
82(lower right & upper left also works). A box is displayed, as below, after the
83first mouse click. After the second the plot is redrawn.
84<P><img alt="tutorial screen dump" src="6c.gif" align=RIGHT>
85<BR clear=all>
86<P><HR noshade width="50%" size="4" align="center"><P>
87
88Note with the plot zoomed in, it can now be seen that
89the lattice parameters do not index the peak 42 degrees very well.
90The computed peak widths agree reasonably well with the observed.
91<P><img alt="tutorial screen dump" src="6d.gif" align=RIGHT>
92<BR clear=all>
93<P><HR noshade width="50%" size="4" align="center"><P>
94
95The fit is even worse at high angle.
96Also, the computed peak widths are much narrower than the observed.
97<P><img alt="tutorial screen dump" src="6e.gif" align=RIGHT>
98<BR clear=all>
99<HR>
100Previous: <A HREF="alumina5.html">
101Initial Fitting: Refine Scale Factor and Background
102</A>
103<BR>
104Next step: <A HREF="alumina7.html">
105Fitting the Unit Cell
106</A>
107
108<HR>
109</blockquote>
110<P><font size=-1><A HREF="MAILTO:crystal@NIST.gov?subject=WWW page <?=$PHP_SELF?>">Comments, corrections or questions: crystal@NIST.gov</A></font><BR>
111<font size=-1><? lastmod(); ?> 
112<BR>$Revision: 930 $ $Date: 2009-12-04 23:14:35 +0000 (Fri, 04 Dec 2009) $</font>
113</body>
114</html>
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