Program f08ftfe ! F08FTF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: blas_zamax_val, f06tff, nag_wp, x04dbf, zhetrd, & zsteqr, zungtr ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Real (Kind=nag_wp) :: r Integer :: i, ifail, info, k, lda, ldz, lwork, n Character (1) :: uplo ! .. Local Arrays .. Complex (Kind=nag_wp), Allocatable :: a(:,:), tau(:), work(:), z(:,:) Real (Kind=nag_wp), Allocatable :: d(:), e(:), rwork(:) Character (1) :: clabs(1), rlabs(1) ! .. Intrinsic Procedures .. Intrinsic :: abs, cmplx, conjg ! .. Executable Statements .. Write (nout,*) 'F08FTF 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(2*n-2)) ! 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 ! The NAG name equivalent of zhetrd is f08fsf Call zhetrd(uplo,n,a,lda,d,e,tau,work,lwork,info) ! Copy A into Z Call f06tff(uplo,n,n,a,lda,z,ldz) ! Form Q explicitly, storing the result in Z ! The NAG name equivalent of zungtr is f08ftf Call zungtr(uplo,n,z,ldz,tau,work,lwork,info) ! Calculate all the eigenvalues and eigenvectors of A ! The NAG name equivalent of zsteqr is f08jsf Call zsteqr('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,99999) d(1:n) Write (nout,*) Flush (nout) ! Normalize the eigenvectors so that the element of largest absolute ! value is real. Do i = 1, n Call blas_zamax_val(n,z(1,i),1,k,r) z(1:n,i) = z(1:n,i)*(conjg(z(k,i))/cmplx(abs(z(k,i)),kind=nag_wp)) End Do ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 Call x04dbf('General',' ',n,n,z,ldz,'Bracketed','F7.4','Eigenvectors', & 'Integer',rlabs,'Integer',clabs,80,0,ifail) End If 99999 Format (8X,4(F7.4,11X:)) End Program f08ftfe