# The Eigenvalue Game

A long time ago, I spent some time working in Matlab, and I discovered a demo called the “Eigenvalue Game” hidden away in one of the toolboxes.

The game works like so: the computer picks a 2×2 matrix `M` (with independent, normally-distributed entries). It then draws the center of the plane ℝ². You can click at any point `v`, and the computer draws the vectors `v` and `M v`. The goal is to click on vectors sufficiently close to eigenvectors of `M`. You can play my recreation of this game below; you can refresh to play again.

An eigenvector of a matrix `M` is a vector `v` such that `M v` is some multiple `λ v` of `v`. So, in the game above, you want to click on the points where the output vector and input vector form a line. I found this game to give me very good intuition for eigenvectors. For example, it became very intuitive how a matrix could lack real eigenvalues: if the matrix rotates its input by a constant angle, the output and input vectors will always be offset from one another.

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