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 pre-defined 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