=begin
  # sample-elementary-divisor01.rb

  require "algebra"
  
  M = SquareMatrix(Rational, 4)
  a = M[
    [2, 0, 0, 0],
    [0, 2, 0, 0],
    [0, 0, 2, 0],
    [5, 0, 0, 2]
  ]
  P = Polynomial(Rational, "x")
  MP = SquareMatrix(P, 4)
  
  ac = a._char_matrix(MP)
  ac.display; puts #=>
  #x - 2,   0,   0,   0
  #  0, x - 2,   0,   0
  #  0,   0, x - 2,   0
  # -5,   0,   0, x - 2
  
  p ac.elementary_divisor #=> [1, x - 2, x - 2, x^2 - 4x + 4]
  
  require "algebra/matrix-algebra-triplet"
  at = ac.to_triplet.e_diagonalize
  
  at.body.display; puts #=>
  #  1,   0,   0,   0
  #  0, x - 2,   0,   0
  #  0,   0, x - 2,   0
  #  0,   0,   0, x^2 - 4x + 4
  
  at.left.display; puts #=>
  #  0,   0,   0, -1/5
  #  0,   1,   0,   0
  #  0,   0,   1,   0
  #  5,   0,   0, x - 2
  
  at.right.display; puts #=>
  #  1,   0,   0, 1/5x - 2/5
  #  0,   1,   0,   0
  #  0,   0,   1,   0
  #  0,   0,   0,   1
  
  p at.left * ac * at.right == at.body #=> true
((<_|CONTENTS>))
=end