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<HTML>
<HEAD>
<TITLE>The Peak Optimiser</TITLE>
</HEAD>
<BODY>
<H1>The Peak Optimiser</H1>
<P>
In instrument control the need arises to optimise a peak with respect to
several variables. Optimising means finding the maximum of the peak with
respect to several variables.
This is usefull during instrument calibration.
Four circle diffractometers use this facility on a day to day basis
for finding and verifying the exact position of reflections. In order to
support both usages a more general module has been implemented. The way of
operation is like this:
<pre>
while errors gt precision and cycles lt maxcycles
for all variables
do a scan
Try find the maximum, two halfwidth points and the peak center.
if failure extend the scan.
if success shift the variable, remember last shift.
If shift lt precicison mark this variable as done
end for
end while
</pre>
Possible outcomes of this procedure are: success, the peak was lost or the
maximum number of cycles was reached. This routine requires that the
instrument is currently placed somewhere on the peak and not miles away.
</P>
<p>
The Peak Optimiser is implemented as an object with the name opti. It
understand the following commands:
<DL>
<DT>opti clear
<DD> clears the optimiser.
<DT>opti addvar name step nStep precision
<DD>This command adds a variable to optimise to the optimiser. The user has
to specify the name of the variable, the step width to use for scanning, the
number of steps needed to cover the full peak when scanning and the
precision which should be achieved when optimising the peak. The step width
and number of steps parameters should cover the whole peak. However, the
Optimiser will extend the scan is the specified range is not sufficient.
<DT>opti run
<DD>Starts the optimiser. It will then optimise the peak. This may take some
time.
</DL>
The behaviour of the optimiser can be configured by modifying some
parameters. The synatx is easy: <b>opti parameter</b> prints the value of the
parameter, <b>opti parameter newval</b> sets a new value for the parameter.
The following parameters are supported:
<DL>
<DT>maxcycles
<DD>The maximum number of cycles the optimiser will run when trying to
optimise a peak. The default is 7.
<DT>threshold
<DD>When a peak cannot be identified after a scan on a variable, the
optimiser will check if there is a peak at all. In order to do that it
searches for a count rate higher then the threshold parameter. If such a
rate cannot be found the optimiser will abort and complain that he lost the
peak.
<DT>channel
<DD>The counter channel to use for scanning. The default is to use the
counter. By modifying this parameter, the optimiser can optimise on a
monitor instead.
<DT>countmode
<DD>The counting mode to use when scanning. Possible values are <b>timer</b> or
<b>monitor</b>.
<DT>preset
<DD>The preset value to use for counting in the scan. Depending on the
status of the countmode parameter this is either a preset time or a preset
monitor.
</DL>
</p>
</BODY>
</HTML>