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<HTML>
<HEAD>
<TITLE>The Online UB Calculation Routine</TITLE>
</HEAD>
<BODY>
<H1>The Online UB Calculation Routine</H1>
<P>
This module allows to calculate the UB matrix from either two reflections and the
cell constants or standalone from three reflections. A little aid for
indexing is implemented too. As usual when dealing with calculations
the common rule: shit in, shit out holds true. In this case this
means that the quality of the UB matrix obtained increases when:
<ul>
<li>Reflections have been centered as accuratly as possible, i.e. with
slits closed and collimators in.
<li>Two theta has been calibrated against a standard beforehand.
<li> The crystal under investigation has been properly centered.
<li>Cell constants and wavelength are accurate.
</ul>
This module is for classic four circle diffraction only.
</P>
<p>
A range of commands allows for reflection and data input and
calculations. For the following discussion it is assumed that the UB
matrix calculation object has been configured into the system under
the name ubcalc.
<dl>
<dt>ubcalc ref1, ref2, ref3 h k l two_theta omega chi phi
<dd>Reflection input for up to three reflections. Miller indices must
be given. When angles are not given, the current position of motors
stt, om, chi, phi is read.
<dt>ubcalc cell a b c alpha beta gamma
<dd>Input of cell constants
<dt>ubcalc ub2ref
<dt>Calculate the UB matrix from ref1, ref2 and the cell constants.
<dt>ubcalc ub3ref
<dd>Calculate the UB matrix from the three reflections ref1, ref2 and
ref3.
<dt>ubcalc listub
<dd>Print the calculated UB matrix
<dt>ubcalc cellub
<dd>Caclulate and print the cell constants as calculated from the UB matrix.
<dt>ubcalc activate
<dd>Copies the UB matrix to the hkl module. The positions of new
reflections can then be calculated with hkl.
<dt>ubcalc index two_theta
<dd>Makes suggestions for possible miller indices matching
two_theta. If two_theta is omitted, the current value of two theta is
read from the motor stt. A brute force search through the space of
possible indices is undertaken using the cell constants given and the
wavelength from the hkl module. This routine is controlled by three
parameters within ubcalc:
<ul>
<li>difftheta, The maximum permissible difference in two_theta
<li>maxindex, The maximum value for miller indices in any direction.
<li>maxlist, The maximum number of suggestions to list.
</ul>
<dt>ubcalc difftheta, maxindex, maxlist value
<dd>Inquire or set the above parameters. For inquiry, give no value,
for setting the parameter give tha name and the value.
<dt>ubcalc list
<dd>Print all the data in ubcalc.
<dt>ubcalc listcell
<dd>Print the cell constants.
<dt>ubcalc listref1, listref2, listref2
<dd>Print reflections 1, 2 or 3
</dl>
</p>
</BODY>
</HTML>