# Introduction

As you run a model, the software uses standard numerical methods to solve the system of equations that comprise your model. In this Chapter, we describe the inner workings of the three numerical methods at your disposal. The Chapter begins with a conceptual overview of how the software solves the equations in a model. Second, the Chapter shows how the three simulation algorithms (Euler's method, 2nd-order Runge-Kutta, and 4th-order Runge-Kutta) are applied to model equations. The Chapter concludes with guidelines for choosing an appropriate step size and integration method in your models.