r8vec_bracket Subroutine

subroutine r8vec_bracket ( n, x, xval, left, right )

  !*****************************************************************************80
  !
  !! R8VEC_BRACKET searches a sorted R8VEC for successive brackets of a value.
  !
  !  Discussion:
  !
  !    An R8VEC is an array of double precision real values.
  !
  !    If the values in the vector are thought of as defining intervals
  !    on the real line, then this routine searches for the interval
  !    nearest to or containing the given value.
  !
  !  Licensing:
  !
  !    This code is distributed under the GNU LGPL license. 
  !
  !  Modified:
  !
  !    06 April 1999
  !
  !  Author:
  !
  !    John Burkardt
  !
  !  Parameters:
  !
  !    Input, integer ( kind = 4 ) N, length of input array.
  !
  !    Input, real ( kind = 8 ) X(N), an array sorted into ascending order.
  !
  !    Input, real ( kind = 8 ) XVAL, a value to be bracketed.
  !
  !    Output, integer ( kind = 4 ) LEFT, RIGHT, the results of the search.
  !    Either:
  !      XVAL < X(1), when LEFT = 1, RIGHT = 2;
  !      X(N) < XVAL, when LEFT = N-1, RIGHT = N;
  !    or
  !      X(LEFT) <= XVAL <= X(RIGHT).
  !
  implicit none

  integer ( kind = 4 ) n

  integer ( kind = 4 ) i
  integer ( kind = 4 ) left
  integer ( kind = 4 ) right
  real    ( kind = 8 ) x(n)
  real    ( kind = 8 ) xval

  do i = 2, n - 1

     if ( xval < x(i) ) then
        left = i - 1
        right = i
        return
     end if

  end do

  left = n - 1
  right = n

  return
end subroutine r8vec_bracket