| 1 | <html> |
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| 2 | <head> |
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| 3 | <META NAME="Author" CONTENT="Brian H. Toby"> |
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| 4 | <title>EXPGUI</title> |
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| 5 | </head> |
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| 6 | <BODY BGCOLOR="#FFFFFF"> |
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| 7 | |
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| 8 | <A HREF=http://www.ncnr.nist.gov> |
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| 10 | alt="Link to NIST Center for Neutron Research home page" |
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| 12 | <A HREF=http://www.nist.gov> |
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| 15 | ALIGN=LEFT></A> |
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| 16 | <CENTER> |
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| 17 | <A Href="http://www.ncnr.nist.gov/programs/crystallography/software/tclpkgs.html"> |
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| 18 | <IMG SRC="tcltklogo100.gif" |
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| 19 | alt="Link to Tcl/Tk information"> |
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| 20 | </CENTER></A> |
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| 21 | <hr> |
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| 22 | |
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| 23 | <TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT> |
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| 24 | <TR><TH><A Href="expgui.html">EXPGUI top</A> |
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| 25 | </TH><TH><A Href="expgui7.html">Next page</A> |
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| 26 | </TH><TH><A Href="expgui5.html">Previous page</A> |
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| 27 | </TH></TR></TABLE><BR CLEAR=ALL> |
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| 28 | |
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| 29 | <center><h1> |
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| 30 | EXPGUI, part 6 |
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| 31 | </h1></center> |
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| 32 | |
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| 33 | <h3>A.6 Constraints pane</h3> |
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| 34 | <DL><DL> |
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| 35 | GSAS offers two types of restraints that can be included in a model. |
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| 36 | So called "soft constraints" or "restraints" penalize the fit if |
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| 37 | aspects of a model (for example, bond lengths) differ from selected values. |
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| 38 | So called "hard constraints" reduce the actual number of |
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| 39 | parameters in a model, |
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| 40 | by grouping parameters so that a single shift (possibly scaled) is |
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| 41 | applied to each parameter in the group. |
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| 42 | The constraints pane is used to set these "hard constraints." |
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| 43 | At this time the only constraints that can be set in EXPGUI are on atomic |
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| 44 | and profile profile (others can be set in EXPEDT). |
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| 45 | <P> |
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| 46 | Note that these constraints are only applied to shifts, but not to the |
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| 47 | actual values. This means that, for example, |
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| 48 | if two atoms |
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| 49 | are constrained so that the shift on their occupancy is the same, but |
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| 50 | the initial occupancies differ, the in occupancy difference will not change |
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| 51 | as the values refine. |
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| 52 | <P> |
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| 53 | Due to the way GSAS implements constraints, a parameter can be included |
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| 54 | in only one constraint. Should one or more parameters be constrained twice, |
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| 55 | the refinement results are unpredictable. |
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| 56 | |
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| 57 | </DL></DL> |
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| 58 | <a name="AtomConstraints"></a> |
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| 59 | <H4>Atom Constraints</H4> |
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| 60 | <DL><DL> |
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| 61 | The atom constraints editing pane appears below. Note that constraints can |
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| 62 | be listed sorted by constraint number, phase number, lowest atom number or |
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| 63 | variable by clicking on the buttons at the top of the pane. |
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| 64 | <P> |
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| 65 | To delete one or more constraints, click on the appropriate checkbuttons in the <B>Delete</B> column and the press the Delete button, below. |
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| 66 | </DL></DL> |
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| 67 | <img SRC="mc.gif" align=TEXTTOP alt="EXPGUI Screen snapshot"> |
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| 68 | <DL><DL> |
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| 69 | <a name="AtomConstraintsError"></a> |
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| 70 | Should parameters be included in more than one constraint, |
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| 71 | an error message is displayed, as shown below. |
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| 72 | Note that the constraint number is displayed as red on the main |
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| 73 | atomic constraints window (see above), if the |
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| 74 | constraint contains a parameter referenced elsewhere. |
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| 75 | |
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| 76 | </DL></DL> |
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| 77 | <img SRC="mcerr.gif" align=TEXTTOP alt="EXPGUI Screen snapshot"> |
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| 78 | <DL><DL> |
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| 79 | <a name="EditAtomConstraints"></a> |
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| 80 | <P> |
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| 81 | <img SRC="mcedit.gif" align=LEFT alt="EXPGUI Screen snapshot"> |
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| 82 | <img SRC="mcvar.gif" align=RIGHT alt="EXPGUI Screen snapshot"> |
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| 83 | When the edit button for a constraint is pressed, the constraint is |
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| 84 | opened for editing. Controls are available to select the phase, variable, |
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| 85 | multiplier and atom(s). Note that for atom selection, use of the control key |
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| 86 | and the left mouse button allow individual atoms to be selected or deselected. |
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| 87 | Shift and the left mouse button allow ranges of atoms to be selected and the |
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| 88 | right mouse button selects all atoms |
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| 89 | <A href="expgui.html#mouseactions">(see Mouse Actions)</A>. |
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| 90 | <P> |
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| 91 | Note that it is inappropriate |
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| 92 | to constrain different types of parameters together, for example X and Uiso. |
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| 93 | The left-most variable button is the "master" which |
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| 94 | determines what variable are allowed in the |
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| 95 | other variable buttons. |
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| 96 | <P> |
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| 97 | When the "New Constraint" button is pressed, a blank constraint editing |
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| 98 | window is opened. Note that any variable to the right may then be selected, |
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| 99 | including two special codes, Uxx and XYZU. XYZU creates four constraints, |
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| 100 | requiring the shifts on x, y, z and Uiso to be the same for all the selected |
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| 101 | atoms. Uxx does the same for the six anisotropic displacement parameters. |
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| 102 | These special codes are valuable for atoms that share a site. |
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| 103 | <P> |
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| 104 | <a name="AtomConstraintsMax"></a> |
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| 105 | Note that only 100 parameters may be included in a single atomic constraint, |
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| 106 | with one exception. When shifts for Uiso |
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| 107 | are constrained to the same value for all atoms in a phase, |
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| 108 | this counts as a single parameter. If more than 100 |
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| 109 | parameters are entered for a constraint, an error message is shown. |
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| 110 | Up to 2000 total atomic constraints may be entered. |
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| 111 | EXPGUI does not warn if you exceed this limit. |
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| 112 | </DL></DL> |
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| 113 | |
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| 114 | <a name="ProfileConstraints"></a> |
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| 115 | <H4>Profile Constraints</H4> |
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| 116 | <DL><DL> |
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| 117 | The profile constraints editing pane appears below. Profile constraints |
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| 118 | are used to relate the shifts applied to profile terms for different |
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| 119 | phase/histogram combinations. Profile terms are identified by number, |
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| 120 | so while EXPEDT allows one to constrain the first profile term for |
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| 121 | a TOF histogram to a the first term in a CW histogram, EXPGUI attempts to |
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| 122 | make this impossible. |
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| 123 | <P> |
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| 124 | To delete one or more constraints, click on the appropriate checkbuttons |
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| 125 | in the <B>Delete</B> column and the press the Delete button, below. |
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| 126 | </DL></DL> |
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| 127 | <img SRC="pc.gif" align=TEXTTOP alt="EXPGUI Screen snapshot"> |
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| 128 | <DL><DL> |
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| 129 | |
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| 130 | <a name="ProfileConstraintErr"></a> |
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| 131 | <img SRC="pcerr.gif" align=LEFT alt="EXPGUI Screen snapshot"> |
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| 132 | Should parameters be included in more than one constraint, |
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| 133 | an error message is displayed, as shown below. |
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| 134 | Note that the constraint number is displayed as red on the main |
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| 135 | profile constraints window (see above), if the |
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| 136 | constraint contains a parameter referenced elsewhere. |
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| 137 | |
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| 138 | <BR CLEAR=LEFT> |
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| 139 | <P> |
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| 140 | <a name="EditProfileConstraints"></a> |
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| 141 | When the edit button for a constraint is pressed, the constraint is |
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| 142 | opened for editing, as shown below. |
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| 143 | Listboxes contain the available phases and histograms. |
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| 144 | Only the histograms of the same data type (TOF, CW or ED) are included, |
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| 145 | but no check is made to ensure that the |
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| 146 | selected phase/histogram combinations |
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| 147 | all have the same profile type. |
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| 148 | Note that for phase and histogram selection, use of the control key |
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| 149 | and the left mouse button allow individual items to be selected or deselected. |
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| 150 | Shift and the left mouse button allow ranges of items to be selected and the |
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| 151 | right mouse button selects all phases or histograms. |
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| 152 | <A href="expgui.html#mouseactions">(see Mouse Actions)</A>. |
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| 153 | <P> |
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| 154 | <img SRC="pcedit.gif" align=TEXTTOP alt="EXPGUI Screen snapshot"> |
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| 155 | <P> |
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| 156 | </DL></DL> |
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| 157 | <a name="NewProfileConstraints"></a> |
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| 158 | <img SRC="pcnew1.gif" align=LEFT alt="EXPGUI Screen snapshot"> |
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| 159 | When the "New Constraint" button is pressed, a window is opened to select |
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| 160 | the histogram and profile function type to be constrained. Note that |
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| 161 | only for profile function #4, where the number of terms depends on the |
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| 162 | phase symmetry, does it matter what phase you select. The available profile |
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| 163 | terms are displayed on the bottom of the window and more than |
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| 164 | one can be selected. |
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| 165 | <BR CLEAR=LEFT> |
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| 166 | <P> |
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| 167 | <DL><DL> |
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| 168 | <img SRC="pcnew2.gif" align=LEFT alt="EXPGUI Screen snapshot"> |
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| 169 | |
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| 170 | After the "Continue" button is pressed, a constraint |
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| 171 | edit window is opened, as shown to the left. |
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| 172 | Listboxes contain the available phases and histograms and |
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| 173 | only the histograms of the selected data type are included, as before. |
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| 174 | Also, for phase and histogram selection, use of the control or shift key |
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| 175 | and the left mouse button allow individual items to be selected or deselected |
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| 176 | and the right mouse button selects all phases or histograms. |
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| 177 | Note that if more than one profile term was selected on the previous window, |
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| 178 | the same set of constraints are for each term. |
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| 179 | <BR CLEAR=LEFT> |
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| 180 | <P> |
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| 181 | <a name="ProfileConstraintsMax"></a> |
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| 182 | Note that only 27 terms can be included in a single profile constraint. |
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| 183 | Also, only like profile terms can be constrained. While GSAS does allow |
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| 184 | different types of profile terms to be constrained together, this does not |
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| 185 | usually make sense and EXPGUI does not allow it. |
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| 186 | </DL></DL> |
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| 187 | <hr> |
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| 188 | <TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT> |
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| 189 | <TR><TH><A Href="expgui.html">EXPGUI top</A> |
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| 190 | </TH><TH><A Href="expgui7.html">Next page</A> |
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| 191 | </TH><TH><A Href="expgui5.html">Previous page</A> |
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| 192 | </TH></TR></TABLE> |
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| 193 | |
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| 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>) |
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| 195 | <br> |
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| 196 | $Revision: 312 $ $Date: 2009-12-04 23:03:57 +0000 (Fri, 04 Dec 2009) $ |
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| 197 | </body> |
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| 198 | </html> |
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