Program f08ygfe

!     F08YGF Example Program Text

!     Mark 27.2 Release. NAG Copyright 2021.

!     .. Use Statements ..
      Use nag_library, Only: dtgsen, nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: pl, pr
      Integer                          :: i, ijob, info, lda, ldb, ldc, ldq,   &
                                          ldz, liwork, lwork, m, n
      Logical                          :: wantq, wantz
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: a(:,:), alphai(:), alphar(:),        &
                                          b(:,:), beta(:), c(:,:), q(:,:),     &
                                          work(:), z(:,:)
      Real (Kind=nag_wp)               :: dif(2)
      Integer, Allocatable             :: iwork(:)
      Logical, Allocatable             :: select(:)
!     .. Executable Statements ..
      Write (nout,*) 'F08YGF Example Program Results'
      Write (nout,*)
      Flush (nout)
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n
      lda = n
      ldb = n
      ldc = n
      ldq = n
      ldz = n
      liwork = (n*n)/2 + 6
      lwork = n*(n+4) + 16
      Allocate (a(lda,n),alphai(n),alphar(n),b(ldb,n),beta(n),c(ldc,n),        &
        q(ldq,n),work(lwork),z(ldz,n),iwork(liwork),select(n))

!     Read A, B, Q, Z and the logical array SELECT from data file

      Read (nin,*)(a(i,1:n),i=1,n)
      Read (nin,*)(b(i,1:n),i=1,n)
      Read (nin,*)(q(i,1:n),i=1,n)
      Read (nin,*)(z(i,1:n),i=1,n)

      Read (nin,*) select(1:n)

!     Set ijob, wantq and wantz
      ijob = 4
      wantq = .True.
      wantz = .True.

!     Reorder the Schur factors A and B and update the matrices
!     Q and Z

!     The NAG name equivalent of dtgsen is f08ygf
      Call dtgsen(ijob,wantq,wantz,select,n,a,lda,b,ldb,alphar,alphai,beta,q,  &
        ldq,z,ldz,m,pl,pr,dif,work,lwork,iwork,liwork,info)

      If (info>0) Then
        Write (nout,99999) info
        Write (nout,*)
        Flush (nout)
      End If

!     Print Results
      Write (nout,99996) 'Number of selected eigenvalues  = ', m
      Write (nout,*)
      Write (nout,*) 'Selected Generalized Eigenvalues'
      Write (nout,*)
      Write (nout,99997)(i,alphar(i)/beta(i),alphai(i)/beta(i),i=1,m)

      Write (nout,*)
      Write (nout,99998) 'Norm estimate of projection onto',                   &
        ' left  eigenspace for selected cluster', 1.0_nag_wp/pl
      Write (nout,*)
      Write (nout,99998) 'Norm estimate of projection onto',                   &
        ' right eigenspace for selected cluster', 1.0_nag_wp/pr
      Write (nout,*)
      Write (nout,99998) 'F-norm based upper bound on', ' Difu', dif(1)
      Write (nout,*)
      Write (nout,99998) 'F-norm based upper bound on', ' Difl', dif(2)

99999 Format (' Reordering could not be completed. INFO = ',I3)
99998 Format (1X,2A,/,1X,1P,E10.2)
99997 Format (1X,I2,1X,'(',1P,E11.4,',',E11.4,')')
99996 Format (1X,A,I4)
    End Program f08ygfe