Program f08gffe ! F08GFF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dopgtr, dsptrd, dsteqr, nag_wp, x04caf ! .. 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 .. Real (Kind=nag_wp), Allocatable :: ap(:), d(:), e(:), q(:,:), tau(:), & work(:) ! .. Executable Statements .. Write (nout,*) 'F08GFF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n ldq = n Allocate (ap(n*(n+1)/2),d(n),e(n),q(ldq,n),tau(n),work(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**T)*A*Q ! The NAG name equivalent of dsptrd is f08gef Call dsptrd(uplo,n,ap,d,e,tau,info) ! Form Q explicitly, storing the result in Q ! The NAG name equivalent of dopgtr is f08gff Call dopgtr(uplo,n,ap,tau,q,ldq,work,info) ! Calculate all the eigenvalues and eigenvectors of A ! The NAG name equivalent of dsteqr is f08jef Call dsteqr('V',n,d,e,q,ldq,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) ! 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 x04caf('General',' ',n,n,q,ldq,'Eigenvectors',ifail) End If 99999 Format (3X,(8F8.4)) End Program f08gffe