2.1.1 :001 > require "matrix"
 => true
2.1.1 :002 > Matrix.identity(5)
 => Matrix[[1, 0, 0, 0, 0], [0, 1, 0, 0, 0], [0, 0, 1, 0, 0], [0, 0, 0, 1, 0], [0, 0, 0, 0, 1]]