Functions

Learning Objectives

Create and save simple functions
Understand the differences between inputs and outputs.

Functions

We have used so far in-built MATLAB functions. In this episode, we will learn to code our own functions, allowing us to repeat code more readily, and make our code more readable. Functions are input-output machines, and with coding, they can be extremely flexible. and allow us to customise with a high degree of control.

Let’s create with an example - a function that calculates the circumference of a circle, $c = 2 \pi r$, where $c$ is the circumference and $r$ is the circle’s radius. First, open up a new m-file.Then, copy the following code:

function circumference = calculate_circumference(radius)
% Function that calculates the circumference of a circle given the radius

circumference = 2*pi*radius;
end

We use function to let MATLAB know this is a function which we can use to call later, and end to designate when we have finished. This function uses one input argument, radius, and has one output argument, circumference.

You must save the m-file before it can be used. It will automatically suggest the function name calculate_circumference.m, allowing us to call it in the command window or other scripts or functions. Once saved, try the function out in the command window:

calculate_circumference(1)

It is always useful to save variables with descriptive names, particularly if sharing your code with others. For example, radius could be shortened to r however it can be difficult to understand what r is without additional context.

Task 4a

Using the last function as a template, now create a function calculate_area that calculates the area of the circle given the radius: $a = \pi r^2$.

Task 4b

Create a function calculate_volume that uses calculate_area and a length, $L$, to calculate the volume of a cylinder: $V = a L$. The function will need to take two arguments like: calculate_volume(radius, length).