Program zupgtr_example ! ZUPGTR Example Program Text ! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com ! .. Use Statements .. Use blas_interfaces, Only: dznrm2 Use lapack_example_aux, Only: nagf_file_print_matrix_complex_gen_comp Use lapack_interfaces, Only: zhptrd, zsteqr, zupgtr Use lapack_precision, Only: dp ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Complex (Kind=dp) :: scal Integer :: i, ifail, info, j, k, ldq, n Character (1) :: uplo ! .. Local Arrays .. Complex (Kind=dp), Allocatable :: ap(:), q(:, :), tau(:), work(:) Real (Kind=dp), Allocatable :: d(:), e(:), rwork(:) Character (1) :: clabs(1), rlabs(1) ! .. Intrinsic Procedures .. Intrinsic :: abs, conjg, maxloc ! .. Executable Statements .. Write (nout, *) 'ZUPGTR Example Program Results' ! Skip heading in data file Read (nin, *) Read (nin, *) n ldq = n Allocate (ap(n*(n+1)/2), q(ldq,n), tau(n), work(n-1), d(n), e(n), rwork( & 2*n-2)) ! Read A from data file Read (nin, *) uplo If (uplo=='U') Then Read (nin, *)((ap(i+j*(j-1)/2),j=i,n), i=1, n) Else If (uplo=='L') Then Read (nin, *)((ap(i+(2*n-j)*(j-1)/2),j=1,i), i=1, n) End If ! Reduce A to tridiagonal form T = (Q**H)*A*Q Call zhptrd(uplo, n, ap, d, e, tau, info) ! Form Q explicitly, storing the result in Q Call zupgtr(uplo, n, ap, tau, q, ldq, work, info) ! Calculate all the eigenvalues and eigenvectors of A Call zsteqr('V', n, d, e, q, ldq, rwork, info) Write (nout, *) If (info>0) Then Write (nout, *) 'Failure to converge.' Else ! Print eigenvalues and eigenvectors Write (nout, *) 'Eigenvalues' Write (nout, 100) d(1:n) Write (nout, *) Flush (nout) ! Normalize the eigenvectors, largest element real Do i = 1, n rwork(1:n) = abs(q(1:n,i)) k = maxloc(rwork(1:n), 1) scal = conjg(q(k,i))/abs(q(k,i))/dznrm2(n, q(1,i), 1) q(1:n, i) = q(1:n, i)*scal End Do ! ifail: behaviour on error exit ! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft ifail = 0 Call nagf_file_print_matrix_complex_gen_comp('General', ' ', n, n, q, & ldq, 'Bracketed', 'F7.4', 'Eigenvectors', 'Integer', rlabs, & 'Integer', clabs, 80, 0, ifail) End If 100 Format (8X, 4(F7.4,11X,:)) End Program