ELI5: Explain Like I'm 5

Decomposition of spectrum (functional analysis)

Have you ever seen a rainbow? Remember how the light from the sun goes through the raindrops and breaks into different colors? This is similar to what happens when we talk about a spectrum in functional analysis.

When we talk about a function in math, we can write it as a sum of simpler functions. This is like taking a complicated picture and breaking it down into smaller pieces that we can understand better.

In functional analysis, we can do something similar with a function called a "linear operator". This is a fancy word for a function that takes in one vector and gives out another vector.

We can break down this linear operator into smaller pieces called "eigenvalues" and "eigenvectors". Just like how a rainbow has different colors, each eigenvalue and eigenvector represents a different aspect of the linear operator.

Think of it like this: imagine you have a bag of marbles. Each marble has a different color and number. You can put all the marbles together in the bag or you can take them out and organize them based on their color or number. When we talk about the decomposition of the spectrum, we are doing the same thing with the linear operator.

By breaking down the linear operator into these smaller pieces, we can understand how it works better and how we can use it in different mathematical problems. It's like taking a puzzle and putting it back together piece by piece to see how it all fits.

So, in short, decomposition of spectrum in functional analysis is a way of breaking down a complicated function into simpler pieces to help us understand it better and use it in different math problems.