'Return the columns associated to self in a design matrix.
If the term has no \'func\' attribute, it returns
``self.namespace[self.termname]``
else, it returns
``self.func(*args, **kw)``'

def __call__(self, *args, **kw):

    if (not hasattr(self, 'func')):
        val = self.namespace[self.termname]
    else:
        val = self.func
    if callable(val):
        if isinstance(val, (Term, Formula)):
            val = copy.copy(val)
            val.namespace = self.namespace
        val = val(*args, **kw)
    val = np.asarray(val)
    return np.squeeze(val)
