Model Settings

The model settings define the core parameters and metadata of the entire model — including the model name, description, simulation time frame, and functions that apply globally across the model.

Field	Input Type	Purpose
Start	Integer	Start time in the chosen time unit
Duration	Integer	Time span over which the simulation should run
Interval	Numeric value	Time steps within the simulation period
Unit	Numeric value (dropdown)	Defines the time dimension
Algorithm	Euler or RK4	Calculation method, depending on the complexity of the model
Globals & Macros	Functions	Function definitions that apply to the entire model

---

Calculation Methods

The Urban Model Builder offers two basic calculation methods, selectable in the global model settings:
the Euler method (Euler) and the Runge–Kutta method (RK4).
Below is a brief explanation of both algorithms.

---

Euler Method

A simple numerical method for solving differential equations.
In System Dynamics models, it is used to simulate the time evolution of dynamic systems.
The simple Euler method calculates the future value of a variable x based on its current value and its rate of change:

$$x(t + \Delta t) = x(t) + \Delta t \cdot \frac{dx}{dt}(t)$$

Where:

$$\begin{aligned} x(t) & : \text{Current value of the state variable (Stock)} \\ \Delta t & : \text{Time step} \\ \frac{dx}{dt}(t) & : \text{Rate of change} \end{aligned}$$

---

Runge–Kutta Method

A more precise numerical method for solving differential equations than Euler’s method.
While the Euler method uses the current rate of change to determine the next state,
the fourth-order Runge–Kutta method (RK4) takes multiple estimates of the rate of change within a single time step and combines them to produce a more accurate prediction.

This method is especially recommended for complex models or simulations over longer time horizons.