Program f08jhfe ! F08JHF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dsbtrd, dstedc, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 Character (1), Parameter :: uplo = 'U' ! .. Local Scalars .. Integer :: i, ifail, info, j, kd, ldab, ldz, & lgn, liwork, lwork, n ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: ab(:,:), d(:), e(:), work(:), z(:,:) Real (Kind=nag_wp) :: rdum(1) Integer :: idum(1) Integer, Allocatable :: iwork(:) ! .. Intrinsic Procedures .. Intrinsic :: ceiling, log, max, min, nint, real ! .. Executable Statements .. Write (nout,*) 'F08JHF Example Program Results' Write (nout,*) ! Skip heading in data file Read (nin,*) Read (nin,*) n, kd ldab = kd + 1 ldz = n lgn = ceiling(log(real(n,kind=nag_wp))/log(2.0E0_nag_wp)) Allocate (ab(ldab,n),d(n),e(n-1),z(ldz,n)) ! Use routine workspace query to get optimal workspace. lwork = -1 liwork = -1 ! The NAG name equivalent of dstedc is f08jhf Call dstedc('V',n,d,e,z,ldz,rdum,lwork,idum,liwork,info) ! Make sure that there is enough workspace. lwork = max(1+3*n+2*n*lgn+4*n*n,nint(rdum(1))) liwork = max(6+6*n+5*n*lgn,idum(1)) Allocate (work(lwork),iwork(liwork)) ! Read the upper or lower triangular part of the band matrix A ! from data file 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 = (Z**T)*A*Z, and form Z ! The NAG name equivalent of dsbtrd is f08hef Call dsbtrd('V',uplo,n,kd,ab,ldab,d,e,z,ldz,work,info) ! Calculate all the eigenvalues and eigenvectors of A, ! from T and Z ! The NAG name equivalent of dstedc is f08jhf Call dstedc('V',n,d,e,z,ldz,work,lwork,iwork,liwork,info) If (info==0) Then ! 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) Else Write (nout,99998) 'Failure in DSTEDC. INFO = ', info End If 99999 Format ((3X,8F8.4)) 99998 Format (1X,A,I10) End Program f08jhfe