code: function ldu(L, D, U, a) {
    L[2] = a[2]/a[0]
    U[0] = a[0]
    U[1] = a[1]
    U[3] = a[3] - L[2] * U[1]
    return [L, D, U]
  }
docs: Returns L, D and U matrices (Lower triangular, Diagonal and Upper triangular) by factorizing the input matrix
  
  @alias mat2.ldu
  @param {mat2} L the lower triangular matrix
  @param {mat2} D the diagonal matrix
  @param {mat2} U the upper triangular matrix
  @param {mat2} a the input matrix to factorize