Program f08sbfe ! F08SBF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: dsygvx, nag_wp, x04caf ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Real (Kind=nag_wp), Parameter :: zero = 0.0_nag_wp Integer, Parameter :: nb = 64, nin = 5, nout = 6 ! .. Local Scalars .. Real (Kind=nag_wp) :: abstol, vl, vu Integer :: i, ifail, il, info, iu, lda, ldb, & ldz, lwork, m, n ! .. Local Arrays .. Real (Kind=nag_wp), Allocatable :: a(:,:), b(:,:), w(:), work(:), z(:,:) Real (Kind=nag_wp) :: dummy(1) Integer, Allocatable :: iwork(:), jfail(:) ! .. Intrinsic Procedures .. Intrinsic :: max, nint ! .. Executable Statements .. Write (nout,*) 'F08SBF Example Program Results' Write (nout,*) ! Skip heading in data file Read (nin,*) Read (nin,*) n lda = n ldb = n ldz = n m = n Allocate (a(lda,n),b(ldb,n),w(n),z(ldz,m),iwork(5*n),jfail(n)) ! Read the lower and upper bounds of the interval to be searched. Read (nin,*) vl, vu ! Use routine workspace query to get optimal workspace. lwork = -1 ! The NAG name equivalent of dsygvx is f08sbf Call dsygvx(1,'Vectors','Values in range','Upper',n,a,lda,b,ldb,vl,vu, & il,iu,abstol,m,w,z,ldz,dummy,lwork,iwork,jfail,info) ! Make sure that there is enough workspace for blocksize nb. lwork = max((nb+3)*n,nint(dummy(1))) Allocate (work(lwork)) ! Read the upper triangular parts of the matrices A and B Read (nin,*)(a(i,i:n),i=1,n) Read (nin,*)(b(i,i:n),i=1,n) ! Set the absolute error tolerance for eigenvalues. With ABSTOL ! set to zero, the default value is used instead abstol = zero ! Solve the generalized symmetric eigenvalue problem ! A*x = lambda*B*x (ITYPE = 1) ! The NAG name equivalent of dsygvx is f08sbf Call dsygvx(1,'Vectors','Values in range','Upper',n,a,lda,b,ldb,vl,vu, & il,iu,abstol,m,w,z,ldz,work,lwork,iwork,jfail,info) If (info>=0 .And. info<=n) Then ! Print solution Write (nout,99999) 'Number of eigenvalues found =', m Write (nout,*) Write (nout,*) 'Eigenvalues' Write (nout,99998) w(1:m) Flush (nout) ! Normalize the eigenvectors Do i = 1, m z(1:n,i) = z(1:n,i)/z(1,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,'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 If (info>n .And. info<=2*n) Then i = info - n Write (nout,99996) 'The leading minor of order ', i, & ' of B is not positive definite' Else Write (nout,99999) 'Failure in DSYGVX. INFO =', info End If 99999 Format (1X,A,I5) 99998 Format (3X,(8F8.4)) 99997 Format (3X,(8I8)) 99996 Format (1X,A,I4,A) End Program f08sbfe