Program f08jlfe ! F08JLF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dstegr, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Real (Kind=nag_wp), Parameter :: vl = 0.0E0_nag_wp Real (Kind=nag_wp), Parameter :: vu = 0.0E0_nag_wp Integer, Parameter :: il = 0, iu = 0, nin = 5, nout = 6 Character (1), Parameter :: range = 'A' ! .. Local Scalars .. Real (Kind=nag_wp) :: abstol Integer :: i, ifail, info, ldz, liwork, lwork, & m, n Character (1) :: jobz ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: d(:), e(:), w(:), work(:), z(:,:) Integer, Allocatable :: isuppz(:), iwork(:) ! .. Executable Statements .. Write (nout,*) 'F08JLF Example Program Results' Write (nout,*) ! Skip heading in data file Read (nin,*) Read (nin,*) n ldz = n liwork = 10*n lwork = 18*n Allocate (d(n),e(n),w(n),work(lwork),z(ldz,n),isuppz(2*n),iwork(liwork)) ! Read the symmetric tridiagonal matrix T from data file, first ! the diagonal elements, then the off diagonal elements and then ! JOBV ('N' - eigenvalues only, 'V' - vectors as well) Read (nin,*) d(1:n) Read (nin,*) e(1:n-1) Read (nin,*) jobz ! Calculate all the eigenvalues of T. Set ABSTOL to zero so that ! the default value is used. abstol = 0.0E0_nag_wp ! The NAG name equivalent of dstegr is f08jlf Call dstegr(jobz,range,n,d,e,vl,vu,il,iu,abstol,m,w,z,ldz,isuppz,work, & lwork,iwork,liwork,info) If (info==0) Then ! Print eigenvalues and eigenvectors Write (nout,*) 'Eigenvalues' Write (nout,99999) w(1:m) Write (nout,*) Flush (nout) ! Standardize the eigenvectors so that first elements are non-negative. Do i = 1, m If (z(1,i)<0.0_nag_wp) z(1:n,i) = -z(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,m,z,ldz,'Eigenvectors',ifail) Else Write (nout,99998) 'Failure to compute an eigenvalue, INFO = ', info End If 99999 Format ((3X,8F8.4)) 99998 Format (1X,A,I10) End Program f08jlfe