subroutine chbmv ( uplo, n, k, alpha, a, lda, x, incx,
     $                   beta, y, incy )
*     .. scalar arguments ..
      complex            alpha, beta
      integer            incx, incy, k, lda, n
      character*1        uplo
*     .. array arguments ..
      complex            a( lda, * ), x( * ), y( * )
*     ..
*
*  purpose
*  =======
*
*  chbmv  performs the matrix-vector  operation
*
*     y := alpha*a*x + beta*y,
*
*  where alpha and beta are scalars, x and y are n element vectors and
*  a is an n by n hermitian band matrix, with k super-diagonals.
*
*  parameters
*  ==========
*
*  uplo   - character*1.
*           on entry, uplo specifies whether the upper or lower
*           triangular part of the band matrix a is being supplied as
*           follows:
*
*              uplo = 'u' or 'u'   the upper triangular part of a is
*                                  being supplied.
*
*              uplo = 'l' or 'l'   the lower triangular part of a is
*                                  being supplied.
*
*           unchanged on exit.
*
*  n      - integer.
*           on entry, n specifies the order of the matrix a.
*           n must be at least zero.
*           unchanged on exit.
*
*  k      - integer.
*           on entry, k specifies the number of super-diagonals of the
*           matrix a. k must satisfy  0 .le. k.
*           unchanged on exit.
*
*  alpha  - complex         .
*           on entry, alpha specifies the scalar alpha.
*           unchanged on exit.
*
*  a      - complex          array of dimension ( lda, n ).
*           before entry with uplo = 'u' or 'u', the leading ( k + 1 )
*           by n part of the array a must contain the upper triangular
*           band part of the hermitian matrix, supplied column by
*           column, with the leading diagonal of the matrix in row
*           ( k + 1 ) of the array, the first super-diagonal starting at
*           position 2 in row k, and so on. the top left k by k triangle
*           of the array a is not referenced.
*           the following program segment will transfer the upper
*           triangular part of a hermitian band matrix from conventional
*           full matrix storage to band storage:
*
*                 do 20, j = 1, n
*                    m = k + 1 - j
*                    do 10, i = max( 1, j - k ), j
*                       a( m + i, j ) = matrix( i, j )
*              10    continue
*              20 continue
*
*           before entry with uplo = 'l' or 'l', the leading ( k + 1 )
*           by n part of the array a must contain the lower triangular
*           band part of the hermitian matrix, supplied column by
*           column, with the leading diagonal of the matrix in row 1 of
*           the array, the first sub-diagonal starting at position 1 in
*           row 2, and so on. the bottom right k by k triangle of the
*           array a is not referenced.
*           the following program segment will transfer the lower
*           triangular part of a hermitian band matrix from conventional
*           full matrix storage to band storage:
*
*                 do 20, j = 1, n
*                    m = 1 - j
*                    do 10, i = j, min( n, j + k )
*                       a( m + i, j ) = matrix( i, j )
*              10    continue
*              20 continue
*
*           note that the imaginary parts of the diagonal elements need
*           not be set and are assumed to be zero.
*           unchanged on exit.
*
*  lda    - integer.
*           on entry, lda specifies the first dimension of a as declared
*           in the calling (sub) program. lda must be at least
*           ( k + 1 ).
*           unchanged on exit.
*
*  x      - complex          array of dimension at least
*           ( 1 + ( n - 1 )*abs( incx ) ).
*           before entry, the incremented array x must contain the
*           vector x.
*           unchanged on exit.
*
*  incx   - integer.
*           on entry, incx specifies the increment for the elements of
*           x. incx must not be zero.
*           unchanged on exit.
*
*  beta   - complex         .
*           on entry, beta specifies the scalar beta.
*           unchanged on exit.
*
*  y      - complex          array of dimension at least
*           ( 1 + ( n - 1 )*abs( incy ) ).
*           before entry, the incremented array y must contain the
*           vector y. on exit, y is overwritten by the updated vector y.
*
*  incy   - integer.
*           on entry, incy specifies the increment for the elements of
*           y. incy must not be zero.
*           unchanged on exit.
*
*
*  level 2 blas routine.
*
*  -- written on 22-october-1986.
*     jack dongarra, argonne national lab.
*     jeremy du croz, nag central office.
*     sven hammarling, nag central office.
*     richard hanson, sandia national labs.