Trend

Calculating a fractional rate of change to be used in forecasting

Diagram

Information

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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 Description: Setting important global variables within a model
	actualTrend	Type: PassThrough Description: Output is identical to input
	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