Program f08fpfe ! F08FPF Example Program Text ! Mark 24 Release. NAG Copyright 2012. ! .. Use Statements .. Use nag_library, Only: blas_zamax_val, nag_wp, x04daf, zheevx ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Real (Kind=nag_wp), Parameter :: zero = 0.0E+0_nag_wp Integer, Parameter :: nb = 64, nin = 5, nout = 6 ! .. Local Scalars .. Real (Kind=nag_wp) :: abstol, r, vl, vu Integer :: i, ifail, il, info, iu, k, lda, ldz, & lwork, m, n ! .. Local Arrays .. Complex (Kind=nag_wp), Allocatable :: a(:,:), work(:), z(:,:) Complex (Kind=nag_wp) :: dummy(1) Real (Kind=nag_wp), Allocatable :: rwork(:), w(:) Integer, Allocatable :: iwork(:), jfail(:) ! .. Intrinsic Procedures .. Intrinsic :: abs, cmplx, conjg, max, nint, real ! .. Executable Statements .. Write (nout,*) 'F08FPF Example Program Results' Write (nout,*) ! Skip heading in data file Read (nin,*) Read (nin,*) n lda = n ldz = n m = n Allocate (a(lda,n),z(ldz,m),rwork(7*n),w(n),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 zheevx is f08fpf Call zheevx('Vectors','Values in range','Upper',n,a,lda,vl,vu,il,iu, & abstol,m,w,z,ldz,dummy,lwork,rwork,iwork,jfail,info) ! Make sure that there is enough workspace for blocksize nb. lwork = max((nb+1)*n,nint(real(dummy(1)))) Allocate (work(lwork)) ! Read the upper triangular part of the matrix A. Read (nin,*)(a(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 Hermitian eigenvalue problem ! The NAG name equivalent of zheevx is f08fpf Call zheevx('Vectors','Values in range','Upper',n,a,lda,vl,vu,il,iu, & abstol,m,w,z,ldz,work,lwork,rwork,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) ! Normalize the eigenvectors so that the element of largest absolute ! value is real. Do i = 1, m Call blas_zamax_val(n,z(1,i),1,k,r) z(1:n,i) = z(1:n,i)*(conjg(z(k,i))/cmplx(abs(z(k,i)),kind=nag_wp)) End Do ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 Call x04daf('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 ZHEEVX. INFO =', info End If 99999 Format (1X,A,I5) 99998 Format (3X,(8F8.4)) 99997 Format (3X,(8I8)) End Program f08fpfe