SSasympOrig              package:stats              R Documentation

_A_s_y_m_p_t_o_t_i_c _R_e_g_r_e_s_s_i_o_n _M_o_d_e_l _t_h_r_o_u_g_h _t_h_e _O_r_i_g_i_n

_D_e_s_c_r_i_p_t_i_o_n:

     This 'selfStart' model evaluates the asymptotic regression
     function through the origin and its gradient.  It has an 'initial'
     attribute that will evaluate initial estimates of the parameters
     'Asym' and 'lrc' for a given set of data.

_U_s_a_g_e:

     SSasympOrig(input, Asym, lrc)

_A_r_g_u_m_e_n_t_s:

   input: a numeric vector of values at which to evaluate the model.

    Asym: a numeric parameter representing the horizontal asymptote.

     lrc: a numeric parameter representing the natural logarithm of the
          rate constant.

_V_a_l_u_e:

     a numeric vector of the same length as 'input'.  It is the value
     of the expression 'Asym*(1 - exp(-exp(lrc)*input))'.  If all of
     the arguments 'Asym' and 'lrc' are names of objects, the gradient
     matrix with respect to these names is attached as an attribute
     named 'gradient'.

_A_u_t_h_o_r(_s):

     Jose Pinheiro and Douglas Bates

_S_e_e _A_l_s_o:

     'nls', 'selfStart'

_E_x_a_m_p_l_e_s:

     Lob.329 <- Loblolly[ Loblolly$Seed == "329", ]
     SSasympOrig( Lob.329$age, 100, -3.2 )  # response only
     Asym <- 100; lrc <- -3.2
     SSasympOrig( Lob.329$age, Asym, lrc ) # response and gradient
     getInitial(height ~ SSasympOrig(age, Asym, lrc), data = Lob.329)
     ## Initial values are in fact the converged values
     fm1 <- nls(height ~ SSasympOrig( age, Asym, lrc), data = Lob.329)
     summary(fm1)

