Program f08jcfe
! F08JCF Example Program Text
! Mark 30.2 Release. NAG Copyright 2024.
! .. Use Statements ..
Use nag_library, Only: dnrm2, dstevd, nag_wp, x04caf
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Real (Kind=nag_wp) :: norm
Integer :: i, ifail, info, ldz, liwork, lwork, &
n
Character (1) :: job
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: d(:), e(:), work(:), z(:,:)
Integer, Allocatable :: iwork(:)
! .. Executable Statements ..
Write (nout,*) 'F08JCF Example Program Results'
! Skip heading in data file
Read (nin,*)
Read (nin,*) n
ldz = n
liwork = 5*n + 3
lwork = n*n + 4*n + 1
Allocate (d(n),e(n-1),work(lwork),z(ldz,n),iwork(liwork))
! Read T from data file
Read (nin,*) d(1:n)
Read (nin,*) e(1:n-1)
Read (nin,*) job
! Calculate all the eigenvalues and eigenvectors of T
! The NAG name equivalent of dstevd is f08jcf
Call dstevd(job,n,d,e,z,ldz,work,lwork,iwork,liwork,info)
Write (nout,*)
If (info>0) Then
Write (nout,*) 'Failure to converge.'
Else
! Print eigenvalues and eigenvectors
Write (nout,*) 'Eigenvalues'
Write (nout,99999) d(1:n)
Write (nout,*)
Flush (nout)
! Normalize the eigenvectors
Do i = 1, n
! The NAG name equivalent of dnrm2 is f06ejf
norm = dnrm2(n,z(1,i),1)
If (z(1,i)<0.0_nag_wp) Then
norm = -norm
End If
z(1:n,i) = z(1:n,i)/norm
End Do
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call x04caf('General',' ',n,n,z,ldz,'Eigenvectors',ifail)
End If
99999 Format (3X,(8F8.4))
End Program f08jcfe