Program f08hefe ! F08HEF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dsbtrd, dsteqr, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Integer :: i, ifail, info, j, kd, ldab, ldq, n Character (1) :: uplo ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: ab(:,:), d(:), e(:), q(:,:), work(:) ! .. Intrinsic Procedures .. Intrinsic :: max, min ! .. Executable Statements .. Write (nout,*) 'F08HEF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n, kd ldab = kd + 1 ldq = n Allocate (ab(ldab,n),d(n),e(n-1),q(ldq,n),work(2*n-2)) ! Read A from data file Read (nin,*) uplo If (uplo=='U') Then Do i = 1, n Read (nin,*)(ab(kd+1+i-j,j),j=i,min(n,i+kd)) End Do Else If (uplo=='L') Then Do i = 1, n Read (nin,*)(ab(1+i-j,j),j=max(1,i-kd),i) End Do End If ! Reduce A to tridiagonal form T = (Q**T)*A*Q (and form Q) ! The NAG name equivalent of dsbtrd is f08hef Call dsbtrd('V',uplo,n,kd,ab,ldab,d,e,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) ! Standardize the eigenvectors so that first elements are non-negative. Do i = 1, n If (q(1,i)<0.0_nag_wp) q(1:n,i) = -q(1:n,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 f08hefe