reset self.__x private attribute

        Parameters
        ----------
        x : numpy.ndarray
        copy : bool
            flag to make a copy of 'x'. Defaule is True
        
        Note
        ----
        makes a copy of 'x' argument

def reset_x(self,x,copy=True):
        """reset self.__x private attribute

        Parameters
        ----------
        x : numpy.ndarray
        copy : bool
            flag to make a copy of 'x'. Defaule is True
        
        Note
        ----
        makes a copy of 'x' argument
        
        """
        assert x.shape == self.shape
        if copy:
            self.__x = x.copy()
        else:
            self.__x = x