bubble_down Subroutine

   SUBROUTINE bubble_down(heap, first)
      !! Balances a heap by bubbling down from the given element.
      TYPE(dbcsr_heap_type), INTENT(INOUT)               :: heap
      INTEGER, INTENT(IN)                                :: first

      INTEGER                                            :: e, left_child, right_child, smallest
      INTEGER(kind=valt)                                 :: left_child_value, min_value, &
                                                            right_child_value
      LOGICAL                                            :: all_done

!
      DBCSR_ASSERT(0 < first .AND. first <= heap%n)

      e = first
      all_done = .FALSE.
      ! Check whether we are finished, i.e,. whether the element to
      ! bubble down is childless.
      DO WHILE (e .LE. get_parent(heap%n) .AND. .NOT. all_done)
         ! Determines which node (current, left, or right child) has the
         ! smallest value.
         smallest = e
         min_value = get_value(heap, e)
         left_child = get_left_child(e)
         IF (left_child .LE. heap%n) THEN
            left_child_value = get_value(heap, left_child)
            IF (left_child_value .LT. min_value) THEN
               min_value = left_child_value
               smallest = left_child
            END IF
         END IF
         right_child = left_child + 1
         IF (right_child .LE. heap%n) THEN
            right_child_value = get_value(heap, right_child)
            IF (right_child_value .LT. min_value) THEN
               min_value = right_child_value
               smallest = right_child
            END IF
         END IF
         !
         CALL dbcsr_heap_swap(heap, e, smallest)
         IF (smallest .EQ. e) THEN
            all_done = .TRUE.
         ELSE
            e = smallest
         END IF
      END DO
   END SUBROUTINE bubble_down