def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def i1beta_torque(i1, beta, torque, title='', ax=0):
    """creates a surface plot of torque vs i1, beta"""
    if ax == 0:
        _create_3d_axis()
        ax = plt.gca()
    azim = 210
    if 0 < np.mean(beta) or -90 > np.mean(beta):
        azim = -60
    unit = 'Nm'
    scale = 1
    if np.min(torque) < -9.9e3 or np.max(torque) > 9.9e3:
        scale = 1e-3
        unit = 'kNm'
    if title:
        _plot_surface(ax, i1, beta, scale*np.asarray(torque),
                      (u'I1/A', u'Beta/°', title),
                      azim=azim)
    else:
        _plot_surface(ax, i1, beta, scale*np.asarray(torque),
                      (u'I1/A', u'Beta/°', u'Torque/{}'.format(unit)),
                      azim=azim)