# Model formulation¶

This section will cover how to formulate mathematical models, including the components of ordinary differential equations.

## What is a state?¶

This video introduces you to the concept of a state in an ODE-based model, useful e.g. in a systems biology project. It allows you know its basic properties, and to identify the states in three versions of writing up a model: state-space form, reaction form, and interaction-graph form.

## What are the parameters?¶

In this video we ask the question: "What are the parameters?", and find that there are three types of them in a state-space model: the kinetic parameters, the initial conditions, and the measurement parameters.

## What are the inputs and outputs?¶

In this video we ask the question: "What are the inputs and outputs?", and find that the inputs are things that we do to the system, and that the outputs are things that we can measure.

## Model from an interaction graph¶

In this video we get to the core of the model formulation task: "How do you write a model in state-space form, from a given interaction-graph?". This video describes the essence of how to formulate a model from an interaction-graph.