twophase                 package:drc                 R Documentation

_T_w_o-_p_h_a_s_e _d_o_s_e-_r_e_s_p_o_n_s_e _m_o_d_e_l

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

     The two-phase dose-response model is a combination of log-logistic
     models that should be useful for describing more complex
     dose-response patterns.

_U_s_a_g_e:

       twophase(fixed = c(NA, NA, NA, NA, NA, NA, NA), 
       names = c("b1", "c1", "d1", "e1", "b2", "d2", "e2"), fctName, fctText)

_A_r_g_u_m_e_n_t_s:

   fixed: numeric vector specifying which parameters are fixed and at
          what value they are fixed.  NAs are used for parameters that
          are not fixed.

   names: a vector of character strings giving the names of the
          parameters (should not contain ":"). The default is
          reasonable (see under 'Usage').

 fctName: optional character string used internally by convenience
          functions.

 fctText: optional character string used internally by convenience
          functions.

_D_e_t_a_i_l_s:

     Following Groot _et al_ (1996) the two-phase model function is
     defined as follows


 f(x) = c + frac{d1-c}{1+exp(b1(log(x)-log(e1)))} + frac{d2}{1+exp(b2(log(x)-log(e2)))}


     For each of the two phases, the parameters have the same
     interpretation as in the ordinary log-logistic model.

_V_a_l_u_e:

     The value returned is a list containing the nonlinear function,
     the self starter function and the parameter names.

_A_u_t_h_o_r(_s):

     Christian Ritz

_R_e_f_e_r_e_n_c_e_s:

     Groot, J. C. J., Cone, J. W., Williams, B. A., Debersaques, F. M.
     A., Lantinga, E. A. (1996) Multiphasic analysis of gas production
     kinetics for in vitro fermentation of ruminant feeds, _Animal Feed
     Science Technology_, *64*, 77-89.

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

     The basic component in the two-phase model is the log-logistic
     model 'llogistic'.

