Zgees Zgees_r Zgeesx Zgeesx_r Zgeev Zgeevx

Zgees() Sub Zgees ( Jobvs As  String, Sort As  String, Selct As  LongPtr, N As  Long, A() As  Complex, Sdim As  Long, W() As  Complex, Vs() As  Complex, Info As  Long  ) (Simple driver) Schur factorization of a complex matrix Purpose This routine computes for an n x n complex nonsymmetric matrix A, the eigenvalues, the Schur form T, and, optionally, the matrix of Schur vectors Z. This gives the Schur factorization A = Z*T*Z^H. Optionally, it also orders the eigenvalues on the diagonal of the Schur form so that selected eigenvalues are at the top left. The leading columns of Z then form an orthonormal basis for the invariant subspace corresponding to the selected eigenvalues. A complex matrix is in Schur form if it is upper triangular. Parameters [in] JobVs = "N": Schur vectors are not computed = "V": Schur vectors are computed [in] Sort Specifies whether or not to order the eigenvalues on the diagonal of the Schur form = "N": Eigenvalues are not ordered = "S": Eigenvalues are ordered (see Selct) [in] Selct Sort = "S": Selct is used to select eigenvalues to sort to the top left of the Schur form.   The eigenvalue W(j) is selected if Selct(W(j)) is true (= 1). Sort = "N": Selct is not referenced. [in] N Order of the matrix A. (N >= 0) (If N = 0, returns without computation) [in,out] A() Array A(LA1 - 1, LA2 - 1) (LA1 >= N, LA2 >= N) [in] N x N matrix A. [out] A() has been overwritten by its Schur form T. [out] Sdim Sort = "N": Sdim = 0. Sort = "S": Sdim = number of eigenvalues for which Selct is true. [out] W() Array W(LW - 1) (LW >= N) W() contains the computed eigenvalues, in the same order that they appear on the diagonal of the output Schur form T. [out] Vs() Array Vs(LVs1 - 1, LVs2 - 1) (LVs1 >= N, LVs2 >= N) Jobvs = "V": Vs() contains the unitary matrix Z of Schur vectors. Jobvs = "N": Vs() is not referenced. [out] Info = 0: Successful exit. = -1: The argument Jobvs had an illegal value. (Jobvs <> "V" nor "N") = -2: The argument Sort had an illegal value. (Sort <> "S" nor "N") = -4: The argument N had an illegal value. (N < 0) = -5: The argument A() is invalid. = -7: The argument W() is invalid. = -8: The argument Vs() is invalid. = i (0 < i <= N): The QR algorithm failed to compute all the eigenvalues. Elements 0 to Ilo-2 and i to N-1 of W() contain those eigenvalues which have converged. If Jobvs = "V", Vs() contains the matrix which reduces A to its partially converged Schur form. = N+1: The eigenvalues could not be reordered because some eigenvalues were too close to separate (the problem is very ill-conditioned). = N+2: After reordering, roundoff changed values of some complex eigenvalues so that leading eigenvalues in the Schur form no longer satisfy Selct = true. This could also be caused by underflow due to scaling. Reference LAPACK Example Program Compute all eigenvalues, Schur form T, and, Schur vectors of the general matrix A, where ( 0.20-0.11i -0.93-0.32i 0.81+0.37i ) A = ( -0.80-0.92i -0.29+0.86i 0.64+0.51i ) ( 0.71+0.59i -0.15+0.19i 0.20+0.94i ) Sub Ex_Zgees() Const N = 3 Dim A(N - 1, N - 1) As Complex, W(N - 1) As Complex Dim Sdim As Long, Vs(N - 1, N - 1) As Complex, Info As Long A(0, 0) = Cmplx(0.2, -0.11): A(0, 1) = Cmplx(-0.93, -0.32): A(0, 2) = Cmplx(0.81, 0.37) A(1, 0) = Cmplx(-0.8, -0.92): A(1, 1) = Cmplx(-0.29, 0.86): A(1, 2) = Cmplx(0.64, 0.51) A(2, 0) = Cmplx(0.71, 0.59): A(2, 1) = Cmplx(-0.15, 0.19): A(2, 2) = Cmplx(0.2, 0.94) Call Zgees("V", "S", AddressOf Selct, N, A(), Sdim, W(), Vs(), Info) Debug.Print "Eigenvalues =" Debug.Print Creal(W(0)), Cimag(W(0)), Creal(W(1)), Cimag(W(1)) Debug.Print Creal(W(2)), Cimag(W(2)) Debug.Print "Schur form T =" Debug.Print Creal(A(0, 0)), Cimag(A(0, 0)), Creal(A(0, 1)), Cimag(A(0, 1)) Debug.Print Creal(A(1, 0)), Cimag(A(1, 0)), Creal(A(1, 1)), Cimag(A(1, 1)) Debug.Print Creal(A(2, 0)), Cimag(A(2, 0)), Creal(A(2, 1)), Cimag(A(2, 1)) Debug.Print Creal(A(0, 2)), Cimag(A(0, 2)) Debug.Print Creal(A(1, 2)), Cimag(A(1, 2)) Debug.Print Creal(A(2, 2)), Cimag(A(2, 2)) Debug.Print "Schur vectors =" Debug.Print Creal(Vs(0, 0)), Cimag(Vs(0, 0)), Creal(Vs(0, 1)), Cimag(Vs(0, 1)) Debug.Print Creal(Vs(1, 0)), Cimag(Vs(1, 0)), Creal(Vs(1, 1)), Cimag(Vs(1, 1)) Debug.Print Creal(Vs(2, 0)), Cimag(Vs(2, 0)), Creal(Vs(2, 1)), Cimag(Vs(2, 1)) Debug.Print Creal(Vs(0, 2)), Cimag(Vs(0, 2)) Debug.Print Creal(Vs(1, 2)), Cimag(Vs(1, 2)) Debug.Print Creal(Vs(2, 2)), Cimag(Vs(2, 2)) Debug.Print "Sdim =", Sdim, "Info =", Info End Sub Function Selct(W As Complex) As Long Selct = 0 If Cimag(W) <> 0 Then Selct = 1 End Function Example Results Eigenvalues = -1.15894122423918 -0.50662892448174 1.05593587167591 0.900255855387815 0.21300535256327 1.29637306909393 Schur form T = -1.15894122423918 -0.50662892448174 2.31358655627147E-02 -0.442808752291521 0 0 1.05593587167591 0.900255855387815 0 0 0 0 -0.644484909898823 -0.733094546116673 0.379301413619788 -0.286520422490734 0.21300535256327 1.29637306909393 Schur vectors = -0.474826946245658 0.464530398931381 -0.103329315153953 0.628092734605153 -0.39444507925059 0.539925475846714 -9.30826818180923E-02 -0.290418461635993 0.264837176182039 -0.203729501266495 -0.367753983153771 0.605452152301986 1.03227229675376E-02 0.391748503946406 2.12814186266949E-02 -0.67781516115713 0.349266221164391 -0.514347515136026 Sdim = 3 Info = 0