braincousens               package:drc               R Documentation

_T_h_e _B_r_a_i_n-_C_o_u_s_e_n_s _h_o_r_m_e_s_i_s _m_o_d_e_l_s

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

     'braincousens' provides a very general way of specifying
     Brain-Cousens'  modified log- logistic model for describing
     hormesis, under various constraints on the parameters.

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

       braincousens(fixed = c(NA, NA, NA, NA, NA), 
       names = c("b", "c", "d", "e", "f"),
       method = c("1", "2", "3", "4"), ssfct = NULL,
       fctName, fctText)

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

   fixed: numeric vector. Specifies which parameters are fixed and at
          what value they are fixed.  NAs for parameter 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'). The order of the parameters
          is: b, c, d, e, f (see under 'Details').

  method: character string indicating the self starter function to use.

   ssfct: a self starter function to be used.

 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:

     The Brain-Cousens model is given by the expression

           f(x) = c + frac{d-c+fx}{1+exp(b(log(x)-log(e)))}

     which is a five-parameter model.

     It is a modification of the four-parameter logistic curve to take
     hormesis into account proposed by Brain and Cousens (1989).

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

     The value returned is a list containing the non-linear function,
     the self starter function,  the parameter names and additional
     model specific objects.

_N_o_t_e:

     This function is for use with the function 'drm'.

     The convenience functions of 'braincousens' are 'BC.4' and 'BC.5'.
     These functions should be used rather than 'braincousens'
     directly.

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

     Christian Ritz

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

     Brain, P. and Cousens, R. (1989) An equation to describe dose
     responses  where there is stimulation of growth at low doses, 
     _Weed Research_, *29*, 93-96.

