Program f08jefe ! F08JEF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dsteqr, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Integer :: i, ifail, info, ldz, n ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: d(:), e(:), work(:), z(:,:) ! .. Executable Statements .. Write (nout,*) 'F08JEF Example Program Results' ! Skip heading in data file Read (nin,*) Read (nin,*) n ldz = n Allocate (d(n),e(n-1),work(2*n-2),z(ldz,n)) ! Read T from data file Read (nin,*) d(1:n) Read (nin,*) e(1:n-1) ! Calculate all the eigenvalues and eigenvectors of T ! The NAG name equivalent of dsteqr is f08jef Call dsteqr('I',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) ! Standardize the eigenvectors so that first elements are non-negative. Do i = 1, n 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,n,z,ldz,'Eigenvectors',ifail) End If 99999 Format (3X,(8F8.4)) End Program f08jefe