Function eigensystem_2 

pub fn eigensystem_2<S>(matrix: Matrix2<S>) -> [Option<(S, Vector2<S>)>; 2]
where
    S: OrderedField + Sqrt + AbsDiffEq<Epsilon = S> + Debug,

Return the (real-valued) eigenvalues and eigenvectors (eigenpairs) of a diagonalizable 2x2 matrix.

Will be ordered by descending eigenvalues.

Returns [Some((0, Vector2::zero())), None] if the matrix is the zero matrix:

let mat = Matrix2::<f32>::zero();
assert_eq!(eigensystem_2 (mat), [Some ((0.0, Vector2::zero())), None]);

Returns [None, None] if eigenvalues are not real values (matrix is orthogonal, e.g. a rotation):

let mat = Matrix2::<f32>::from_row_arrays ([
  [0.0, -1.0],
  [1.0,  0.0]
]);
assert_eq!(eigensystem_2 (mat), [None, None]);

Returns [Some, None] if the matrix has only one eigenvector direction (matrix is not diagonalizable):

let mat = Matrix2::<f32>::from_row_arrays ([
  [ 3.0, 1.0],
  [-1.0, 1.0]
]);
assert!(matches!(eigensystem_2 (mat), [Some(_), None]));