ELI5: Explain Like I'm 5

Pseudo-differential operator

Okay, let's try to explain this in a way that a 5-year-old can understand.

Imagine you have a toy box filled with different toys. You can think of these toys like different mathematical functions – each one has its own special way of moving and changing. Now let's say you want to combine two different toys together to make a new toy. You might take a truck and a helicopter and put them together to make a flying truck!

A pseudo-differential operator is a lot like combining two toys together. It's a way of taking two different mathematical functions and putting them together to make a new function. But instead of just sticking them together like you would with toys, a pseudo-differential operator does some special things to the functions first.

It's kind of like when you mix two different colors of paint together. You can't just put them together and hope they look good – you have to mix them in a certain way to get the color you want. A pseudo-differential operator works like that, but with functions instead of colors.

So why do we need to do this? Well, sometimes we need to change the way a function works in order to solve a problem. Maybe we need it to move faster or slower, or we need it to be more spread out or more concentrated. A pseudo-differential operator lets us do all of those things by combining different functions together in a special way.

It's a bit like using magic to solve a math problem – you have to wave a wand (the pseudo-differential operator) and say some special words (the math behind it) to make it work. But once you know how to do it, you can use it to solve all sorts of tricky problems!