ELI5: Explain Like I'm 5

Direct integral

A direct integral is like a big box that contains lots of little boxes inside it. Each little box has its own set of numbers that represent something important, and the big box is like a way to combine all of those smaller sets into one big set.

When we talk about direct integrals in math, we're usually talking about functions. A function is like a machine that takes in a number and spits out another number. But sometimes, we need to work with functions that have different numbers of inputs or outputs.

Imagine you had a bunch of different machines in your toy box. Some have one button you can press, some have two, and some have three. Each machine does something different, but they all take in numbers and give you a new number when you push their buttons.

To combine all of these machines into one big machine, we can use a direct integral. We start by making a list of all the machines we want to combine. Then, we create a new machine that has one button for each of the buttons on the other machines. So if we have three machines with one button each, we make a new machine with three buttons.

When we push one of the buttons on the big machine, it tells us which little machine to use and which button on that machine to push. We use the little machine to calculate the output, and we get back a new number.

So in the end, the direct integral is like a big box that contains lots of little boxes with different numbers of buttons. When we push a button on the big box, it tells us which little box to use and which button to push. We use the little box to calculate something important, and we get a new number as a result.