STEM help / Data dialogs

Time series / Dual S-Curve

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

Alignment

Determines what point in the Base Period or Period the Base value or corresponding values is/are associated with.

Default: End for demand-related inputs, but Beginning for tariffs and cost trends.

Step (1)

Constrains the dynamics of any time-series input to yield a constant value for quarterly, annual or even indefinite periods.

Default: Day (no constraint is applied: values evolve smoothly).

Birth Period

Enables you to ‘switch on’ the curve (from zero). This can be a year, a quarter, a month, or even a fully-qualified date.

Default: Y0.

Death Period

Enables you to ‘switch off’ the curve (from zero). This can be a year, a quarter, a month, or even a fully-qualified date.

Default: Y-1.

 

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