Program f08qyfe

!     F08QYF Example Program Text

!     Mark 27.3 Release. NAG Copyright 2021.

!     .. Use Statements ..
      Use nag_library, Only: f06uaf, nag_wp, x02ajf, ztrevc, ztrsna
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: eps, tnorm
      Integer                          :: i, info, ldt, ldvl, ldvr, ldwork, m, &
                                          n
!     .. Local Arrays ..
      Complex (Kind=nag_wp), Allocatable :: t(:,:), vl(:,:), vr(:,:),          &
                                          work(:,:)
      Real (Kind=nag_wp), Allocatable  :: rwork(:), s(:), sep(:)
      Logical                          :: select(1)
!     .. Executable Statements ..
      Write (nout,*) 'F08QYF Example Program Results'
      Write (nout,*)
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n
      ldt = n
      ldvl = n
      ldvr = n
      ldwork = n
      Allocate (t(ldt,n),vl(ldvl,n),vr(ldvr,n),work(ldwork,n+1),rwork(n),s(n), &
        sep(n))

!     Read T from data file

      Read (nin,*)(t(i,1:n),i=1,n)

!     Calculate the left and right eigenvectors of T

!     The NAG name equivalent of ztrevc is f08qxf
      Call ztrevc('Both','All',select,n,t,ldt,vl,ldvl,vr,ldvr,n,m,work,rwork,  &
        info)

!     Estimate condition numbers for all the eigenvalues and right
!     eigenvectors of T

!     The NAG name equivalent of ztrsna is f08qyf
      Call ztrsna('Both','All',select,n,t,ldt,vl,ldvl,vr,ldvr,s,sep,n,m,work,  &
        ldwork,rwork,info)

!     Print condition numbers of eigenvalues and right eigenvectors

      Write (nout,*) 'S'
      Write (nout,99999) s(1:m)
      Write (nout,*)
      Write (nout,*) 'SEP'
      Write (nout,99999) sep(1:m)

!     Calculate approximate error estimates (using the 1-norm)

      eps = x02ajf()
      tnorm = f06uaf('1-norm',n,n,t,ldt,rwork)
      Write (nout,*)
      Write (nout,*) 'Approximate error estimates for eigenvalues ',           &
        'of T (machine-dependent)'
      Write (nout,99999)(eps*tnorm/s(i),i=1,m)
      Write (nout,*)
      Write (nout,*) 'Approximate error estimates for right ',                 &
        'eigenvectors of T (machine-dependent)'
      Write (nout,99999)(eps*tnorm/sep(i),i=1,m)

99999 Format ((3X,1P,7E11.1))
    End Program f08qyfe