Program f08gtfe ! F08GTF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: nag_wp, x04dbf, zhptrd, zsteqr, zupgtr ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Integer :: i, ifail, info, j, ldq, n Character (1) :: uplo ! .. Local Arrays .. Complex (Kind=nag_wp), Allocatable :: ap(:), q(:,:), tau(:), work(:) Real (Kind=nag_wp), Allocatable :: d(:), e(:), rwork(:) Character (1) :: clabs(1), rlabs(1) ! .. Executable Statements .. Write (nout,*) 'F08GTF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n ldq = n Allocate (ap(n*(n+1)/2),q(ldq,n),tau(n),work(n-1),d(n),e(n),rwork(2*n-2) & ) ! Read A from data file Read (nin,*) uplo If (uplo=='U') Then Read (nin,*)((ap(i+j*(j-1)/2),j=i,n),i=1,n) Else If (uplo=='L') Then Read (nin,*)((ap(i+(2*n-j)*(j-1)/2),j=1,i),i=1,n) End If ! Reduce A to tridiagonal form T = (Q**H)*A*Q ! The NAG name equivalent of zhptrd is f08gsf Call zhptrd(uplo,n,ap,d,e,tau,info) ! Form Q explicitly, storing the result in Q ! The NAG name equivalent of zupgtr is f08gtf Call zupgtr(uplo,n,ap,tau,q,ldq,work,info) ! Calculate all the eigenvalues and eigenvectors of A ! The NAG name equivalent of zsteqr is f08jsf Call zsteqr('V',n,d,e,q,ldq,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 Do i = 1, n q(1:n,i) = q(1:n,i)/q(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,n,q,ldq,'Bracketed','F7.4','Eigenvectors', & 'Integer',rlabs,'Integer',clabs,80,0,ifail) End If 99999 Format (8X,4(F7.4,11X:)) End Program f08gtfe