Constant

The Constant function returns a fixed value throughout the simulation. It is often used to supply a constant input (e.g., temperature threshold, fixed growth rate, photoperiod sensitivity) to other models in APSIM Next Gen.

Overview

This function provides a simple way to input a value that does not change over time. It can be added wherever a numerical input is required and does not depend on environmental conditions, crop stage, or other simulation variables.

In APSIM NG, Constant is widely used as a basic building block within more complex functions, or to define cultivar-specific constants (e.g., base temperature = 0 °C, leaf width = 10 mm).

Inputs

  • FixedValue: The constant numerical value returned.
  • Units (optional): The units associated with the value (e.g., °C, mm/day).

Methodology

This function always returns the same value, specified by the user in the FixedValue property. It does not depend on any conditions or crop stages.

Mathematically: \[ \text{Value} = \text{FixedValue} \]

It implements the IFunction interface, making it compatible with any APSIM component that accepts functions as inputs.

Events

Events Listened For

No events are listened by this function.

Events Raised to

No events are raised by this function.

Properties

Configurable and Reportable Properties

Property Type Description
FixedValue double The constant value to return
Units string Optional units associated with the value

Read-Only Reportable Properties

No read-only properties are available for this function.

User Interface

Constant can be added as a child of any function-based node (e.g., PhaseLookupValue, MultiplyFunction, AddFunction) in the model tree. To use:

  1. Right-click the parent node.
  2. Select “Add Model…”.
  3. Search for “Constant” and select it.
  4. Enter the desired numeric value and optional units.

Practical Example

To define a base temperature of 0 °C used in a thermal time calculation:

  • Add a Constant function under a ThermalTime node.
  • Set FixedValue to 0.0
  • Set Units to °C

This constant will now serve as the threshold temperature in the growing degree-day calculation.

See Also