Think Eigenvector (Mona Lisa Restored) Tile

If you think in terms of eigenvectors, you'll enjoy any of these gifts featuring a mapping of a restored Mona Lisa along with the caption "Think Eigenvector". In this shear mapping the red arrow changes direction but the blue arrow does not. The eigenvectors of a square matrix are the non-zero vectors that, after being multiplied by the matrix, remain parallel to the original vector. Thus, the blue arrow is an eigenvector, with eigenvalue 1 as its length is unchanged.