Polynomial background function

Polynomial background component is able to characterize the continuous, slowly changing background under peaks.

It is implemented as a second order polynomial in the region, so constant, slanting or curved (parabolic) background may be modeled with it, freely combining its counterparts. As a background function, its area will not be summed up to the peak area. It may have at most three fitted parameters: Level, Slope and Curvature.

The picture shows a sample polynomial background with Level=10, Slope=0.5, Curve=-0.03 parameters.

Counts from the polynomial background may be calculated by the following formula at channel RegionPos:

where

	RegionPos:	Channel position within the fitted region (first channel of the region is 0)
	Level:	Constant background level
	Slope:	Background slope (may be positive or negative)
	Curve:	Background curvature (may be positive or negative)