def broadcastable_to_str(b):
    """Return string representation of broadcastable."""
    named_broadcastable = {(): 'scalar', (False,): 'vector', (False, True):
        'col', (True, False): 'row', (False, False): 'matrix'}
    if b in named_broadcastable:
        bcast = named_broadcastable[b]
    else:
        bcast = ''
    return bcast
