ELI5: Explain Like I'm 5

Level-index arithmetic

Okay kiddo, let's imagine you have a lot of toy blocks, and you want to organize them so it's easy to find the one you want to play with. One way to do this is to put all the blue blocks in one pile, all the red blocks in another pile, and so on. This is called sorting them by color.

Level-index arithmetic is kind of like sorting blocks by color, but with numbers.

To understand this, let's first talk about how we normally count. When we count, we use a system called "base 10". That means we have 10 digits to work with: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. When we have more than 9 things, we start using two digits: 10, 11, 12, and so on.

But what if we wanted to count in a different way, with more or fewer digits? That's where level-index arithmetic comes in.

In level-index arithmetic, we start by choosing a "base" or "radix". This is like choosing a color for our blocks. Let's say we pick 3 as our base. That means we only have three digits to work with: 0, 1, and 2. When we get to 3, we start using two digits: 10, 11, 12, and so on.

But instead of using the digits 0, 1, and 2, we can represent them as levels, like steps on a staircase. Level 0 is the bottom step, level 1 is the next step up, and so on. So if we had 5 blocks and we were counting in base 3, we would say "level 2, level 2, level 1", which means 5 in regular base 10 counting.

Level-index arithmetic can be useful in computer science and other fields where we need to work with numbers in different bases, or where we want to use a smaller number of symbols to represent numbers. Just like sorting blocks by color makes it easier to find the one you want, using level-index arithmetic can make it easier to work with certain types of numbers.