Program f08fgfe ! F08FGF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dormtr, dstebz, dstein, dsytrd, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Real (Kind=nag_wp), Parameter :: zero = 0.0E0_nag_wp Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Real (Kind=nag_wp) :: vl, vu Integer :: i, ifail, info, lda, ldc, lwork, m, & n, nsplit Character (1) :: uplo ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: a(:,:), c(:,:), d(:), e(:), tau(:), & w(:), work(:) Integer, Allocatable :: iblock(:), ifailv(:), isplit(:), & iwork(:) ! .. Executable Statements .. Write (nout,*) 'F08FGF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n lda = n ldc = n lwork = 64*n Allocate (a(lda,n),c(ldc,n),d(n),e(n),tau(n),w(n),work(lwork),iblock(n), & ifailv(n),isplit(n),iwork(3*n)) ! 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**T)*A*Q Call dsytrd(uplo,n,a,lda,d,e,tau,work,lwork,info) ! Calculate the two smallest eigenvalues of T (same as A) ! The NAG name equivalent of dstebz is f08jjf Call dstebz('I','B',n,vl,vu,1,2,zero,d,e,m,nsplit,w,iblock,isplit,work, & iwork,info) Write (nout,*) If (info>0) Then Write (nout,*) 'Failure to converge.' Else Write (nout,*) 'Eigenvalues' Write (nout,99999) w(1:m) ! Calculate the eigenvectors of T, storing the result in C ! The NAG name equivalent of dstein is f08jkf Call dstein(n,d,e,m,w,iblock,isplit,c,ldc,work,iwork,ifailv,info) If (info>0) Then Write (nout,*) 'Failure to converge.' Else ! Calculate the eigenvectors of A = Q * (eigenvectors of T) ! The NAG name equivalent of dormtr is f08fgf Call dormtr('Left',uplo,'No transpose',n,m,a,lda,tau,c,ldc,work, & lwork,info) ! Print eigenvectors Write (nout,*) Flush (nout) ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 Call x04caf('General',' ',n,m,c,ldc,'Eigenvectors',ifail) End If End If 99999 Format (3X,(9F8.4)) End Program f08fgfe