A Dual S-Curve is the sum of two S-Curves, and is specified by two parallel sets of S-Curve parameters. You can use a negative curve to make the series into a ‘hump’, or you can use two positive curves, with different Base Periods to specify a series which rises, levels off, and then rises again. Each series is defined by the following parameters:
Saturation
The asymptotic value of the series, as time either increases or decreases, according to the relative sizes of Value A and Value B.
Default: 0.0.
Base Period (2)
A reference period before and at which the series is constant at zero, or the Saturation level, again according to the relative sizes of Value A and Value B.
Default: Y-1.
Period A
The period in which Value A applies. This can be a year, a quarter, a month, or even a fully-qualified date.
Default: Y0.
Value A
The value in Period A. This is the first reference point for the series.
Default: 0.
Period B
The period in which Value B applies. This can be a year, a quarter, a month, or even a fully-qualified date.
Default: Y0.
Value B
The value in Period B. This is the second reference point for the series.
Given the two specific reference points for the series, STEM fits an S-shaped curve through these two points to match the Saturation level and Base Period. If the first value is greater than the second, you can define a curve that starts at the Saturation level, and then falls, representing a declining Service.
Default: 0.
Options