

_A_d_d _a _S_t_r_a_i_g_h_t _L_i_n_e _t_o _a _P_l_o_t

     abline(a, b, ...)
     abline(h=, ...)
     abline(v=, ...)
     abline(coef=, ...)
     abline(reg=, ...)

_D_e_s_c_r_i_p_t_i_o_n:

     This function adds one or more straight lines through
     the current plot.  The first form above specifies the
     line in intercept/slope form (alternatively `a' can be
     specified on its own and is taken to contain the slope
     and intercept in vector form).  The `h=' and `v=' forms
     draw horizontal and vertical lines at the specified
     coordinates.  The `coef' form specifies the line by a
     vector containing the slope and intercept.  `reg' is a
     regression object which contains `reg$coef'.  If it is
     of length 1 then the value is taken to be the slope of
     a line through the origin, otherwise, the first 2
     values are taken to be the slope and intercept.

     The graphical parameters `col' and `lty' can be speci-
     fied as arguments to `abline'; see `par' for details.

_S_e_e _A_l_s_o:

     `lines' and `segments' for connected and arbitrary
     lines given by their endpoints.  `par'.

_E_x_a_m_p_l_e_s:

     data(cars)
     z <- lm(dist ~ speed, data = cars)
     plot(cars)
     abline(z)

