Program dopmtr_example ! DOPMTR Example Program Text ! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com ! .. Use Statements .. Use lapack_example_aux, Only: nagf_blas_damax_val, & nagf_file_print_matrix_real_gen Use lapack_interfaces, Only: dopmtr, dsptrd, dstebz, dstein Use lapack_precision, Only: dp ! .. Implicit None Statement .. Implicit None ! .. Parameters .. Real (Kind=dp), Parameter :: zero = 0.0E0_dp Integer, Parameter :: nin = 5, nout = 6 ! .. Local Scalars .. Real (Kind=dp) :: r, vl, vu Integer :: i, ifail, info, j, k, ldc, m, n, nsplit Character (1) :: uplo ! .. Local Arrays .. Real (Kind=dp), Allocatable :: ap(:), c(:, :), d(:), e(:), tau(:), w(:), & work(:) Integer, Allocatable :: iblock(:), ifailv(:), isplit(:), iwork(:) ! .. Executable Statements .. Write (nout, *) 'DOPMTR Example Program Results' ! Skip heading in data file Read (nin, *) Read (nin, *) n ldc = n Allocate (ap(n*(n+1)/2), c(ldc,n), d(n), e(n), tau(n), w(n), work(5*n), & iblock(n), ifailv(n), isplit(n), iwork(3*n)) ! 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**T)*A*Q Call dsptrd(uplo, n, ap, d, e, tau, info) ! Calculate the two smallest eigenvalues of T (same as A) Call dstebz('I', 'B', n, vl, vu, 1, 2, zero, d, e, m, nsplit, w, iblock, & isplit, work, iwork, info) Write (nout, *) If (info>0) Then Write (nout, *) 'Failure to converge.' Else Write (nout, *) 'Eigenvalues' Write (nout, 100) w(1:m) ! Calculate the eigenvectors of T, storing the result in C Call dstein(n, d, e, m, w, iblock, isplit, c, ldc, work, iwork, & ifailv, info) If (info>0) Then Write (nout, *) 'Failure to converge.' Else ! Calculate the eigenvectors of A = Q * (eigenvectors of T) Call dopmtr('Left', uplo, 'No transpose', n, m, ap, tau, c, ldc, & work, info) ! Print eigenvectors Write (nout, *) Flush (nout) ! Normalize the eigenvectors Do i = 1, m Call nagf_blas_damax_val(n, c(1,i), 1, k, r) If (c(k,i)