Program zpteqr_example
! ZPTEQR 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: zhetrd, zlacpy, zpteqr, zungtr
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, k, lda, ldz, lwork, n
Character (1) :: uplo
! .. Local Arrays ..
Complex (Kind=dp), Allocatable :: a(:, :), tau(:), work(:), z(:, :)
Real (Kind=dp), Allocatable :: d(:), e(:), rwork(:)
Character (1) :: clabs(1), rlabs(1)
! .. Intrinsic Procedures ..
Intrinsic :: abs, conjg, maxloc
! .. Executable Statements ..
Write (nout, *) 'ZPTEQR Example Program Results'
! Skip heading in data file
Read (nin, *)
Read (nin, *) n
lda = n
ldz = n
lwork = 64*n
Allocate (a(lda,n), tau(n), work(lwork), z(ldz,n), d(n), e(n), &
rwork(4*n))
! Read A from data file
Read (nin, *) uplo
If (uplo=='U') Then
Read (nin, *)(a(i,i:n), i=1, n)
Else If (uplo=='L') Then
Read (nin, *)(a(i,1:i), i=1, n)
End If
! Reduce A to tridiagonal form T = (Q**H)*A*Q
Call zhetrd(uplo, n, a, lda, d, e, tau, work, lwork, info)
! Copy A into Z
Call zlacpy(uplo, n, n, a, lda, z, ldz)
! Form Q explicitly, storing the result in Z
Call zungtr(uplo, n, z, ldz, tau, work, lwork, info)
! Calculate all the eigenvalues and eigenvectors of A
Call zpteqr('V', n, d, e, z, ldz, 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(z(1:n,i))
k = maxloc(rwork(1:n), 1)
scal = conjg(z(k,i))/abs(z(k,i))/dznrm2(n, z(1,i), 1)
z(1:n, i) = z(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, z, &
ldz, 'Bracketed', 'F7.4', 'Eigenvectors', 'Integer', rlabs, &
'Integer', clabs, 80, 0, ifail)
End If
100 Format (8X, 4(F7.4,11X,:))
End Program