Trend

Calculating a fractional rate of change to be used in forecasting

Diagram

Information

This information is part of the Business Simulation Library (BSL).

The Trend component represents forecasting in behavioral models and has been proposed by Sterman [3, pp. 634 - 638]. The basic idea is rather intuitive: Forecasters perceive a present condition of some input as a smoothed input (ppc), while they also perceive the historic or reference condition (rc) as a smooth of their current perception.

Dividing the diffence between the current condition and the reference condition by the reference condition will determine the fractional increase. A further division by the time horizon for the reference condition will then turn this into a fractional rate. The thus calculated rate of change (i.e., the indicated trend) may then again be smoothed, if smoothTrend = true.

Parameters (7)

initialTrend	Value: 0 Type: Rate (1/s) Description: Initial trend
tppc	Value: 1 Type: Time (s) Description: Averaging time for perception of current quantity (i.e., the present condition)
thrc	Value: 1 Type: Time (s) Description: Time horizon for reference condition
tpt	Value: 1 Type: Time (s) Description: Time to perceive the trend (i.e., there is gradual adaptation to a new trend)
smoothTrend	Value: false Type: Boolean Description: = true, if the calculated trend is to be smoothed
reportPPC	Value: false Type: Boolean Description: = true, if the perceived present conditon is to be reported
init	Value: modelSettings.init Type: InitializationOptions Description: Provide InitializationOptions (Free, FixedValue, SteadyState)

Connectors (3)

	y	Type: RealOutput Description: Information output signal
	u	Type: RealInput Description: Current value as basis for trend formulation
	y_ppc	Type: RealOutput Description: Report the perceived present condition (optional)

Type: RealOutput

Description: Information output signal

Type: RealInput

Description: Current value as basis for trend formulation

y_ppc

Type: RealOutput

Description: Report the perceived present condition (optional)

Components (11)

	modelSettings	Type: ModelSettings
	actualTrend	Type: PassThrough
	rc	Type: Smooth Description: Reference condition for calculating the fractional trend
	ppc	Type: Smooth Description: Perceived present condition
	parTPPC	Type: ConstantConverterTime Description: Time to perceive present condition
	parTHRC	Type: ConstantConverterTime Description: Time horizon for the reference condition (duration of trend formulation)
	parTPT	Type: ConstantConverterTime Description: Time to perceive the trend (i.e., adjustment time)
	perceivedTrend	Type: Smooth Description: Perceived growth rate
	indicatedTrend	Type: Division_Guarded Description: Indicated fractional growth rate (trend)
	delta	Type: Gap Description: Difference between perceived present condition and reference condition
	rcTimesTHRC	Type: Product_2 Description: Referenc condition times time horizon for reference condition