Program f08nufe ! F08NUF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: nag_wp, x04dbf, zgehrd, zhsein, zhseqr, zunmhr ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Real (Kind=nag_wp) :: thresh Integer :: i, ifail, info, lda, ldc, ldh, ldvl, & ldz, lwork, m, n ! .. Local Arrays .. Complex (Kind=nag_wp), Allocatable :: a(:,:), c(:,:), h(:,:), tau(:), & vl(:,:), w(:), work(:), z(:,:) Real (Kind=nag_wp), Allocatable :: rwork(:) Integer, Allocatable :: ifaill(:), ifailr(:) Logical, Allocatable :: select(:) Character (1) :: clabs(1), rlabs(1) ! .. Intrinsic Procedures .. Intrinsic :: aimag, real ! .. Executable Statements .. Write (nout,*) 'F08NUF Example Program Results' Flush (nout) ! Skip heading in data file Read (nin,*) Read (nin,*) n ldz = 1 lda = n ldc = n ldh = n ldvl = n lwork = 64*n Allocate (a(lda,n),c(ldc,n),h(ldh,n),tau(n),vl(ldvl,n),w(n),work(lwork), & z(ldz,1),rwork(n),ifaill(n),ifailr(n),select(n)) ! Read A from data file Read (nin,*)(a(i,1:n),i=1,n) Read (nin,*) thresh ! Reduce A to upper Hessenberg form H = (Q**H)*A*Q ! The NAG name equivalent of zgehrd is f08nsf Call zgehrd(n,1,n,a,lda,tau,work,lwork,info) ! Copy A to H h(1:n,1:n) = a(1:n,1:n) ! Calculate the eigenvalues of H (same as A) ! The NAG name equivalent of zhseqr is f08psf Call zhseqr('Eigenvalues','No vectors',n,1,n,h,ldh,w,z,ldz,work,lwork, & info) Write (nout,*) If (info>0) Then Write (nout,*) 'Failure to converge.' Else Write (nout,*) 'Eigenvalues' Write (nout,99999)(' (',real(w(i)),',',aimag(w(i)),')',i=1,n) Flush (nout) Do i = 1, n select(i) = real(w(i)) < thresh End Do ! Calculate the eigenvectors of H (as specified by SELECT), ! storing the result in C ! The NAG name equivalent of zhsein is f08pxf Call zhsein('Right','QR','No initial vectors',select,n,a,lda,w,vl, & ldvl,c,ldc,n,m,work,rwork,ifaill,ifailr,info) ! Calculate the eigenvectors of A = Q * (eigenvectors of H) ! The NAG name equivalent of zunmhr is f08nuf Call zunmhr('Left','No transpose',n,m,1,n,a,lda,tau,c,ldc,work,lwork, & info) ! Print eigenvectors Write (nout,*) Flush (nout) ! Normalize the eigenvectors Do i = 1, m c(1:n,i) = c(1:n,i)/c(1,i) 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,m,c,ldc,'Bracketed','F7.4', & 'Contents of array C','Integer',rlabs,'Integer',clabs,80,0,ifail) End If 99999 Format ((3X,4(A,F7.4,A,F7.4,A:))) End Program f08nufe