Program f08hbfe ! F08HBF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dsbevx, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Real (Kind=nag_wp), Parameter :: zero = 0.0E+0_nag_wp Integer, Parameter :: nin = 5, nout = 6 Character (1), Parameter :: uplo = 'U' ! .. Local Scalars .. Real (Kind=nag_wp) :: abstol, vl, vu Integer :: i, ifail, il, info, iu, j, kd, ldab, & ldq, ldz, m, n ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: ab(:,:), q(:,:), w(:), work(:), z(:,:) Integer, Allocatable :: iwork(:), jfail(:) ! .. Intrinsic Procedures .. Intrinsic :: max, min ! .. Executable Statements .. Write (nout,*) 'F08HBF Example Program Results' Write (nout,*) ! Skip heading in data file Read (nin,*) Read (nin,*) n, kd ldab = kd + 1 ldq = n ldz = n m = n Allocate (ab(ldab,n),q(ldq,n),w(n),work(7*n),z(ldz,m),iwork(5*n), & jfail(n)) ! Read the lower and upper bounds of the interval to be searched, ! and read the upper or lower triangular part of the matrix A ! from data file Read (nin,*) vl, vu If (uplo=='U') Then Read (nin,*)((ab(kd+1+i-j,j),j=i,min(n,i+kd)),i=1,n) Else If (uplo=='L') Then Read (nin,*)((ab(1+i-j,j),j=max(1,i-kd),i),i=1,n) End If ! Set the absolute error tolerance for eigenvalues. With ABSTOL ! set to zero, the default value is used instead abstol = zero ! Solve the band symmetric eigenvalue problem ! The NAG name equivalent of dsbevx is f08hbf Call dsbevx('Vectors','Values in range',uplo,n,kd,ab,ldab,q,ldq,vl,vu, & il,iu,abstol,m,w,z,ldz,work,iwork,jfail,info) If (info>=0) Then ! Print solution Write (nout,99999) 'Number of eigenvalues found =', m Write (nout,*) Write (nout,*) 'Eigenvalues' Write (nout,99998) 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) If (info>0) Then Write (nout,99999) 'INFO eigenvectors failed to converge, INFO =', & info Write (nout,*) 'Indices of eigenvectors that did not converge' Write (nout,99997) jfail(1:m) End If Else Write (nout,99999) 'Failure in DSBEVX. INFO =', info End If 99999 Format (1X,A,I5) 99998 Format (3X,(8F8.4)) 99997 Format (3X,(8I8)) End Program f08hbfe