ELI5: Explain Like I'm 5

Muirhead's inequality

Muirhead's inequality is a rule that helps us compare the sizes of different groups of numbers. Imagine you and your friends have some delicious candies. You might want to know if you have more candies than your friend. If you both have the same kind of candies, you can just count how many each of you has. But what if you have different kinds of candies altogether? This is where Muirhead's inequality comes in handy.

Muirhead's inequality says that if you have two groups of numbers, and one group is more "spread out" than the other, then the less spread-out group is always smaller or equal to the more spread-out group. This is kind of like saying that if you have two jars of candies, and one jar has candies of different kinds and lots of them, and the other jar has fewer candies that are all the same kind, then the first jar must have more candies in total.

So, what does "more spread out" mean? It means that the numbers in the group have a wider range. For example, let's say you have two groups of three numbers: {2, 3, 5} and {3, 3, 4}. The second group has smaller range (the difference between the largest and smallest number) compared to the first group, so Muirhead's inequality tells us that the first group is always larger than or equal to the second group.

Muirhead's inequality is especially helpful when we are dealing with groups of numbers that have different sizes or when we need to compare larger sets of numbers. By comparing how "spread out" the sets of numbers are, we can quickly see which one is larger, without having to count each individual number.