Coxeter matrix

A Coxeter matrix is like a map for shapes that have a lot of angles. Imagine you have a toy set with a bunch of blocks that have different angles on them. If you wanted to know how to put the blocks together to make a certain shape, you would need to follow a map or a set of instructions. This is what a Coxeter matrix does. It tells you which angles are important and how they relate to each other when you're trying to make a certain shape. So if you're trying to make a triangle out of those blocks, the Coxeter matrix would tell you how to put them together in the right way. It's kind of like a puzzle!