Program zpteqr_example ! ZPTEQR 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: zhetrd, zlacpy, zpteqr, zungtr 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, k, lda, ldz, lwork, n Character (1) :: uplo ! .. Local Arrays .. Complex (Kind=dp), Allocatable :: a(:, :), tau(:), work(:), z(:, :) Real (Kind=dp), Allocatable :: d(:), e(:), rwork(:) Character (1) :: clabs(1), rlabs(1) ! .. Intrinsic Procedures .. Intrinsic :: abs, conjg, maxloc ! .. Executable Statements .. Write (nout, *) 'ZPTEQR Example Program Results' ! Skip heading in data file Read (nin, *) Read (nin, *) n lda = n ldz = n lwork = 64*n Allocate (a(lda,n), tau(n), work(lwork), z(ldz,n), d(n), e(n), & rwork(4*n)) ! Read A from data file Read (nin, *) uplo If (uplo=='U') Then Read (nin, *)(a(i,i:n), i=1, n) Else If (uplo=='L') Then Read (nin, *)(a(i,1:i), i=1, n) End If ! Reduce A to tridiagonal form T = (Q**H)*A*Q Call zhetrd(uplo, n, a, lda, d, e, tau, work, lwork, info) ! Copy A into Z Call zlacpy(uplo, n, n, a, lda, z, ldz) ! Form Q explicitly, storing the result in Z Call zungtr(uplo, n, z, ldz, tau, work, lwork, info) ! Calculate all the eigenvalues and eigenvectors of A Call zpteqr('V', n, d, e, z, ldz, 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(z(1:n,i)) k = maxloc(rwork(1:n), 1) scal = conjg(z(k,i))/abs(z(k,i))/dznrm2(n, z(1,i), 1) z(1:n, i) = z(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, z, & ldz, 'Bracketed', 'F7.4', 'Eigenvectors', 'Integer', rlabs, & 'Integer', clabs, 80, 0, ifail) End If 100 Format (8X, 4(F7.4,11X,:)) End Program