_W_a_r_n_i_n_g _M_e_s_s_a_g_e_s
	
	     warning(message)
	
	_D_e_s_c_r_i_p_t_i_o_n:
	
	     warning prints the message given as its argument.
	
	_E_x_a_m_p_l_e_s:
	
	     if(eigenval < 1.e-7) warning("system near singular")