'A flattened array of all parameter values in all parameter sets.
Fittable parameters maintain this list and fitters modify it.'

@property
def parameters(self):

    if (not self.param_names):
        return self._parameters
    start = self._param_metrics[self.param_names[0]][u'slice'].start
    stop = self._param_metrics[self.param_names[(-1)]][u'slice'].stop
    return self._parameters[start:stop]
