Program dsbevd_example ! DSBEVD Example Program Text ! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com ! .. Use Statements .. Use lapack_example_aux, Only: nagf_file_print_matrix_real_gen Use lapack_interfaces, Only: dsbevd Use lapack_precision, Only: dp ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Integer :: i, ifail, info, j, kd, ldab, ldz, liwork, lwork, n Character (1) :: job, uplo ! .. Local Arrays .. Real (Kind=dp), Allocatable :: ab(:, :), w(:), work(:), z(:, :) Integer, Allocatable :: iwork(:) ! .. Intrinsic Procedures .. Intrinsic :: max, min ! .. Executable Statements .. Write (nout, *) 'DSBEVD Example Program Results' ! Skip heading in data file Read (nin, *) Read (nin, *) n, kd ldab = kd + 1 ldz = n liwork = 5*n + 3 lwork = 2*n*n + 5*n + 1 Allocate (ab(ldab,n), w(n), work(lwork), z(ldz,n), iwork(liwork)) ! Read A from data file Read (nin, *) uplo If (uplo=='U') Then Do i = 1, n Read (nin, *)(ab(kd+1+i-j,j), j=i, min(n,i+kd)) End Do Else If (uplo=='L') Then Do i = 1, n Read (nin, *)(ab(1+i-j,j), j=max(1,i-kd), i) End Do End If Read (nin, *) job ! Calculate all the eigenvalues and eigenvectors of A Call dsbevd(job, uplo, n, kd, ab, ldab, w, z, ldz, work, lwork, iwork, & liwork, info) Write (nout, *) If (info>0) Then Write (nout, *) 'Failure to converge.' Else ! Print eigenvalues and eigenvectors Write (nout, *) 'Eigenvalues' Write (nout, 100) w(1:n) Write (nout, *) Flush (nout) ! Standardize the eigenvectors so that first elements are non-negative. Do i = 1, n If (z(1,i)<0.0_dp) Then z(1:n, i) = -z(1:n, i) End If 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_real_gen('General', ' ', n, n, z, ldz, & 'Eigenvectors', ifail) End If 100 Format (3X, (8F8.4)) End Program