Program f08fqfe
! F08FQF Example Program Text
! Mark 30.0 Release. NAG Copyright 2024.
! .. Use Statements ..
Use nag_library, Only: nag_wp, x04daf, zheevd, zscal
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Integer :: i, ifail, info, k, lda, liwork, &
lrwork, lwork, n
Character (1) :: job, uplo
! .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: a(:,:), work(:)
Real (Kind=nag_wp), Allocatable :: rwork(:), w(:)
Integer, Allocatable :: iwork(:)
! .. Intrinsic Procedures ..
Intrinsic :: abs, cmplx, conjg, maxloc
! .. Executable Statements ..
Write (nout,*) 'F08FQF Example Program Results'
! Skip heading in data file
Read (nin,*)
Read (nin,*) n
lda = n
liwork = 5*n + 3
lrwork = 2*n*n + 5*n + 1
lwork = n*(n+2)
Allocate (a(lda,n),work(lwork),rwork(lrwork),w(n),iwork(liwork))
Read (nin,*) uplo
! Read A from data file
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
Read (nin,*) job
! Calculate all the eigenvalues and eigenvectors of A
! The NAG name equivalent of zheevd is f08fqf
Call zheevd(job,uplo,n,a,lda,w,work,lwork,rwork,lrwork,iwork,liwork, &
info)
Write (nout,*)
If (info>0) Then
Write (nout,*) 'Failure to converge.'
Else
! Print eigenvalues and eigenvectors
Write (nout,*) 'Eigenvalues'
Do i = 1, n
Write (nout,99999) i, w(i)
End Do
Write (nout,*)
Flush (nout)
! Normalize the eigenvectors so that the element of largest absolute
! value is real.
Do i = 1, n
rwork(1:n) = abs(a(1:n,i))
k = maxloc(rwork(1:n),1)
Call zscal(n,conjg(a(k,i))/cmplx(abs(a(k,i)),kind=nag_wp),a(1,i),1)
End Do
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call x04daf('General',' ',n,n,a,lda,'Eigenvectors',ifail)
End If
99999 Format (3X,I5,5X,2F8.4)
End Program f08fqfe