Module zgges_mod
! ZGGES Example Program Module:
! .. Implicit None Statement ..
Implicit None
! .. Accessibility Statements ..
Private
Public :: selctg
Contains
Function selctg(a, b)
! .. Use Statements ..
Use lapack_precision, Only: dp
! .. Implicit None Statement ..
Implicit None
! .. Function Return Value ..
Logical :: selctg
! .. Scalar Arguments ..
Complex (Kind=dp), Intent (In) :: a, b
! .. Intrinsic Procedures ..
Intrinsic :: abs
! .. Executable Statements ..
Continue
! Dummy function - it is not called by ZGGES when sorting is not required.
selctg = (abs(a)<6.0_dp*abs(b))
Return
End Function
End Module
Program zgges_example
! ZGGES Example Program Text
! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com
! .. Use Statements ..
Use blas_interfaces, Only: zgemm
Use lapack_example_aux, Only: nagf_sort_realvec_rank, &
nagf_file_print_matrix_complex_gen_comp, &
nagf_sort_cmplxvec_rank_rearrange
Use lapack_interfaces, Only: zgges, zlange
Use lapack_precision, Only: dp
Use zgges_mod, Only: selctg
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nb = 64, nin = 5, nout = 6
Logical, Parameter :: chkfac = .False., prmat = .False.
! .. Local Scalars ..
Complex (Kind=dp) :: alph, bet
Real (Kind=dp) :: normd, norme
Integer :: i, ifail, info, lda, ldb, ldc, ldd, lde, ldvsl, ldvsr, lwork, &
n, sdim
Logical :: factor
! .. Local Arrays ..
Complex (Kind=dp), Allocatable :: a(:, :), alpha(:), b(:, :), beta(:), &
c(:, :), d(:, :), e(:, :), vsl(:, :), vsr(:, :), work(:)
Complex (Kind=dp) :: wdum(1)
Real (Kind=dp), Allocatable :: rwork(:)
Integer, Allocatable :: irank(:)
Logical, Allocatable :: bwork(:)
Character (1) :: clabs(1), rlabs(1)
! .. Intrinsic Procedures ..
Intrinsic :: abs, all, cmplx, epsilon, max, nint, real
! .. Executable Statements ..
Write (nout, *) 'ZGGES Example Program Results'
Write (nout, *)
Flush (nout)
! Skip heading in data file
Read (nin, *)
Read (nin, *) n
lda = n
ldb = n
ldc = n
ldd = n
lde = n
ldvsl = n
ldvsr = n
Allocate (a(lda,n), alpha(n), b(ldb,n), beta(n), c(ldc,n), d(ldd,n), &
e(lde,n), vsl(ldvsl,n), vsr(ldvsr,n), rwork(8*n), bwork(n), irank(n))
! Use routine workspace query to get optimal workspace.
lwork = -1
Call zgges('Vectors (left)', 'Vectors (right)', 'No sort', selctg, n, a, &
lda, b, ldb, sdim, alpha, beta, vsl, ldvsl, vsr, ldvsr, wdum, lwork, &
rwork, bwork, info)
! Make sure that there is enough workspace for block size nb.
lwork = max((nb+1)*n, nint(real(wdum(1))))
Allocate (work(lwork))
! Read in the matrices A and B
Read (nin, *)(a(i,1:n), i=1, n)
Read (nin, *)(b(i,1:n), i=1, n)
! Copy A and B into D and E respectively
d(1:n, 1:n) = a(1:n, 1:n)
e(1:n, 1:n) = b(1:n, 1:n)
If (prmat) Then
! Print matrices A and B
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call nagf_file_print_matrix_complex_gen_comp('General', ' ', n, n, a, &
lda, 'Bracketed', 'F8.4', 'Matrix A', 'Integer', rlabs, 'Integer', &
clabs, 80, 0, ifail)
Write (nout, *)
Flush (nout)
ifail = 0
Call nagf_file_print_matrix_complex_gen_comp('General', ' ', n, n, b, &
ldb, 'Bracketed', 'F8.4', 'Matrix B', 'Integer', rlabs, 'Integer', &
clabs, 80, 0, ifail)
Write (nout, *)
Flush (nout)
End If
factor = .True.
! Find the generalized Schur form
Call zgges('Vectors (left)', 'Vectors (right)', 'No sort', selctg, n, a, &
lda, b, ldb, sdim, alpha, beta, vsl, ldvsl, vsr, ldvsr, work, lwork, &
rwork, bwork, info)
If (info>0) Then
Write (nout, 100) 'Failure in ZGGES. INFO =', info
factor = .False.
Else If (chkfac) Then
! Compute A - Q*S*Z^H from the factorization of (A,B) and store in
! matrix D
alph = cmplx(1, kind=dp)
bet = cmplx(0, kind=dp)
Call zgemm('N', 'N', n, n, n, alph, vsl, ldvsl, a, lda, bet, c, ldc)
alph = cmplx(-1, kind=dp)
bet = cmplx(1, kind=dp)
Call zgemm('N', 'C', n, n, n, alph, c, ldc, vsr, ldvsr, bet, d, ldd)
! Compute B - Q*T*Z^H from the factorization of (A,B) and store in
! matrix E
alph = cmplx(1, kind=dp)
bet = cmplx(0, kind=dp)
Call zgemm('N', 'N', n, n, n, alph, vsl, ldvsl, b, ldb, bet, c, ldc)
alph = cmplx(-1, kind=dp)
bet = cmplx(1, kind=dp)
Call zgemm('N', 'C', n, n, n, alph, c, ldc, vsr, ldvsr, bet, e, lde)
! Find norms of matrices D and E and warn if either is too large
normd = zlange('O', ldd, n, d, ldd, rwork)
norme = zlange('O', lde, n, e, lde, rwork)
If (normd>epsilon(1.0E0_dp)**0.75_dp) Then
Write (nout, *) 'Norm of A-(Q*S*Z^H) is much greater than 0.'
factor = .False.
End If
If (norme>epsilon(1.0E0_dp)**0.75_dp) Then
Write (nout, *) 'Norm of B-(Q*T*Z^H) is much greater than 0.'
factor = .False.
End If
End If
If (factor) Then
! Sort and print generalized eigenvalues if none are infinite
If (all(real(beta(1:n))>0.0_dp)) Then
work(1:n) = alpha(1:n)/beta(1:n)
rwork(1:n) = abs(work(1:n))
! Rank eigenvalues
ifail = 0
Call nagf_sort_realvec_rank(rwork, 1, n, 'Descending', irank, ifail)
! Sort eigenvalues in work(1:n)
Call nagf_sort_cmplxvec_rank_rearrange(work, 1, n, irank, ifail)
Write (nout, *) 'Generalized Eigenvalues'
Do i = 1, n
Write (nout, 110) i, work(i)
End Do
End If
Else
Write (nout, *) 'Schur factorization has failed.'
End If
100 Format (1X, A, I4)
110 Format (1X, I2, 3X, '(', F6.2, ',', F6.2, ')')
End Program