Bhattacharyya angle

The Bhattacharyya angle measures how similar two vectors are. It's like a measure of how close two things are to each other. Imagine that two vectors are like two people standing almost side-by-side; the Bhattacharyya angle is a way of measuring how close they are standing: if they are closer together then the angle is small, and if they are farther away then the angle is larger. It's like a way of measuring how related the two vectors are.