Program f08jdfe ! F08JDF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dstevr, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Real (Kind=nag_wp), Parameter :: zero = 0.0_nag_wp Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Real (Kind=nag_wp) :: abstol, vl, vu Integer :: ifail, il, info, iu, ldz, liwork, & lwork, m, n ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: d(:), e(:), w(:), work(:), z(:,:) Real (Kind=nag_wp) :: rdum(1) Integer :: idum(1) Integer, Allocatable :: isuppz(:), iwork(:) ! .. Intrinsic Procedures .. Intrinsic :: max, nint ! .. Executable Statements .. Write (nout,*) 'F08JDF Example Program Results' Write (nout,*) ! Skip heading in data file and read N and the lower and upper ! indices of the eigenvalues to be found Read (nin,*) Read (nin,*) n, il, iu ldz = n m = n Allocate (d(n),e(n-1),w(n),z(ldz,m),isuppz(2*n)) ! Use routine workspace query to get optimal workspace. lwork = -1 liwork = -1 ! The NAG name equivalent of dstevr is f08jdf Call dstevr('Vectors','Indices',n,d,e,vl,vu,il,iu,abstol,m,w,z,ldz, & isuppz,rdum,lwork,idum,liwork,info) ! Make sure that there is enough workspace for blocksize nb. lwork = max(20*n,nint(rdum(1))) liwork = max(10*n,idum(1)) Allocate (work(lwork),iwork(liwork)) ! Read the diagonal and off-diagonal elements of the matrix A ! from data file Read (nin,*) d(1:n) Read (nin,*) e(1:n-1) ! Set the absolute error tolerance for eigenvalues. With ABSTOL ! set to zero, the default value is used instead abstol = zero ! Solve the symmetric tridiagonal eigenvalue problem ! The NAG name equivalent of dstevr is f08jdf Call dstevr('Vectors','Indices',n,d,e,vl,vu,il,iu,abstol,m,w,z,ldz, & isuppz,work,lwork,iwork,liwork,info) If (info==0) Then ! Print solution Write (nout,*) 'Selected eigenvalues' Write (nout,99999) w(1:m) 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,m,z,ldz,'Selected eigenvectors',ifail) Else Write (nout,99998) 'Failure in DSTEVR. INFO =', info End If 99999 Format (3X,(8F8.4)) 99998 Format (1X,A,I5) End Program f08jdfe