Program zupgtr_example
! ZUPGTR Example Program Text
! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com
! .. Use Statements ..
Use blas_interfaces, Only: dznrm2
Use lapack_example_aux, Only: nagf_file_print_matrix_complex_gen_comp
Use lapack_interfaces, Only: zhptrd, zsteqr, zupgtr
Use lapack_precision, Only: dp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Complex (Kind=dp) :: scal
Integer :: i, ifail, info, j, k, ldq, n
Character (1) :: uplo
! .. Local Arrays ..
Complex (Kind=dp), Allocatable :: ap(:), q(:, :), tau(:), work(:)
Real (Kind=dp), Allocatable :: d(:), e(:), rwork(:)
Character (1) :: clabs(1), rlabs(1)
! .. Intrinsic Procedures ..
Intrinsic :: abs, conjg, maxloc
! .. Executable Statements ..
Write (nout, *) 'ZUPGTR Example Program Results'
! Skip heading in data file
Read (nin, *)
Read (nin, *) n
ldq = n
Allocate (ap(n*(n+1)/2), q(ldq,n), tau(n), work(n-1), d(n), e(n), rwork( &
2*n-2))
! Read A from data file
Read (nin, *) uplo
If (uplo=='U') Then
Read (nin, *)((ap(i+j*(j-1)/2),j=i,n), i=1, n)
Else If (uplo=='L') Then
Read (nin, *)((ap(i+(2*n-j)*(j-1)/2),j=1,i), i=1, n)
End If
! Reduce A to tridiagonal form T = (Q**H)*A*Q
Call zhptrd(uplo, n, ap, d, e, tau, info)
! Form Q explicitly, storing the result in Q
Call zupgtr(uplo, n, ap, tau, q, ldq, work, info)
! Calculate all the eigenvalues and eigenvectors of A
Call zsteqr('V', n, d, e, q, ldq, rwork, info)
Write (nout, *)
If (info>0) Then
Write (nout, *) 'Failure to converge.'
Else
! Print eigenvalues and eigenvectors
Write (nout, *) 'Eigenvalues'
Write (nout, 100) d(1:n)
Write (nout, *)
Flush (nout)
! Normalize the eigenvectors, largest element real
Do i = 1, n
rwork(1:n) = abs(q(1:n,i))
k = maxloc(rwork(1:n), 1)
scal = conjg(q(k,i))/abs(q(k,i))/dznrm2(n, q(1,i), 1)
q(1:n, i) = q(1:n, i)*scal
End Do
! 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, q, &
ldq, 'Bracketed', 'F7.4', 'Eigenvectors', 'Integer', rlabs, &
'Integer', clabs, 80, 0, ifail)
End If
100 Format (8X, 4(F7.4,11X,:))
End Program