Calculated Intensity Weight (CalculatedIWeight)
This object is placed under an Experimental Plot object to
allow a estimated error or weight to be specified in Contour Fitting as a function of
intensity or frequency. The value of the expression is taken as
the estimated error of the observation. A possible function might
be:
5+sqrt(y)
where 5 represents the average error in the
baseline, and the error increases as the square root of the
signal, typical of photon counting. The function will be evaluated
for each data point. If present, two additional curves are plotted
either side of the extra curve, indicating +/ the estimated
error. Notes:
 The function is held in the comment field for the object; in
the constants window an
enlarged text window replaces the normal comments window.
 See expressions for more
details on the format of expressions.
 The predefined variables are listed below; any unknown
variables in the function are automatically created as
parameters on simulating, or on right clicking on the node and
selecting "Check Variables"
 Unwanted variables that are no longer in the expression can be
removed by right clicking on the parameter and selecting remove.
Built In Variables
i

Point number

x

The x (Position)
value

y

The y (Intensity)
value

w

The estimated error in the
position (not currently used in contour fits).

wy

The estimated error in the
intensity, if present in the original data, 1 otherwise. 
n

The number of points.

Settings
Active 
True if object is to be used 
nDebug 
Set non zero to write information to the log window on
each use  See expressions 