#### Introduction

- The greek letter sigma allows us to describe a range of values, and then add them all together.
- For example, if we want to add the numbers from 1 to 4, we can write:
- This expands to: 1 + 2 + 3 + 4
- The value of n starts at 1 (written under the sigma), and ends on 4 (written above the sigma).

#### A more complex sum

- In the introductory example, we simply put
**n** after our sigma, however we can write more complex equations too: - This would expand to:

#### Summing sets

- If we have a set of numbers, for example:
**S** = [2, 5, 3], then we can sum it with: - Where
**|S|** is the length of the set, and **S**_{n} is the n^{th} value of **S**. - This is often simplified to:

#### code (Python)

```
numbers = [1,2,3,4]
summed = sum(numbers)
print(summed) # prints 10
```