'Fix a parameter'

@fixed.setter
def fixed(self, value):

    if (self._model is not None):
        if (not isinstance(value, bool)):
            raise TypeError(u'Fixed    can    be    True    or    False')
        self._model._constraints[u'fixed'][self._name] = value
    else:
        raise AttributeError(u"can't    set    attribute    'fixed'    on    Parameter    definition")
