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.

See also

TrendBasedForecast, Smooth

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)

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

Used in Components (1)

TrendBasedForecast

BusinessSimulation.MoleculesOfStructure.InformationProcessing

Trend-based forecast for an exponentially growing quantity