Program f08fffe ! F08FFF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dorgtr, dsteqr, dsytrd, f06qff, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Integer :: i, ifail, info, lda, ldz, lwork, n Character (1) :: uplo ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: a(:,:), d(:), e(:), tau(:), work(:), & z(:,:) ! .. Executable Statements .. Write (nout,*) 'F08FFF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n lda = n ldz = n lwork = 64*n Allocate (a(lda,n),d(n),e(n),tau(n),work(lwork),z(ldz,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 ! The NAG name equivalent of dsytrd is f08fef Call dsytrd(uplo,n,a,lda,d,e,tau,work,lwork,info) ! Copy A into Z Call f06qff(uplo,n,n,a,lda,z,ldz) ! Form Q explicitly, storing the result in Z ! The NAG name equivalent of dorgtr is f08fff Call dorgtr(uplo,n,z,ldz,tau,work,lwork,info) ! Calculate all the eigenvalues and eigenvectors of A ! The NAG name equivalent of dsteqr is f08jef Call dsteqr('V',n,d,e,z,ldz,work,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) ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 Call x04caf('General',' ',n,n,z,ldz,'Eigenvectors',ifail) End If 99999 Format (3X,(8F8.4)) End Program f08fffe