code: def unfixed_param_array(self):
          
          if self.constraints[__fixed__].size !=0:
              fixes = np.ones(self.size).astype(bool)
              fixes[self.constraints[__fixed__]] = FIXED
              return self._param_array_[fixes]
          else:
              return self._param_array_
docs: Array representing the parameters of this class.
          There is only one copy of all parameters in memory, two during optimization.
  
          !WARNING!: setting the parameter array MUST always be done in memory:
          m.param_array[:] = m_copy.param_array