Program zhbevd_example

!     ZHBEVD 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
      Use lapack_interfaces, Only: zhbevd
      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, kd, ldab, ldz, liwork, lrwork, lwork, n
      Character (1) :: job, uplo
!     .. Local Arrays ..
      Complex (Kind=dp), Allocatable :: ab(:, :), work(:), z(:, :)
      Real (Kind=dp), Allocatable :: rwork(:), w(:)
      Integer, Allocatable :: iwork(:)
!     .. Intrinsic Procedures ..
      Intrinsic :: abs, conjg, max, maxloc, min
!     .. Executable Statements ..
      Write (nout, *) 'ZHBEVD Example Program Results'
!     Skip heading in data file
      Read (nin, *)
      Read (nin, *) n, kd
      ldab = n
      ldz = n
      liwork = 5*n + 3
      lrwork = 2*n*n + 5*n + 1
      lwork = 2*n*n
      Allocate (ab(ldab,n), work(lwork), z(ldz,n), rwork(lrwork), w(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 zhbevd(job, uplo, n, kd, ab, ldab, w, z, ldz, work, lwork, rwork, &
        lrwork, iwork, liwork, info)

      Write (nout, *)
      If (info>0) Then
        Write (nout, *) 'Failure to converge.'
      Else

!       Print eigenvalues and eigenvectors

        Write (nout, *) 'Eigenvalues'
        Do i = 1, n
          Write (nout, 100) i, w(i)
        End Do
        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('General', ' ', n, n, z, ldz, &
          'Eigenvectors', ifail)

      End If

100   Format (3X, I5, 5X, 2F8.4)
    End Program