EXD                   package:drc                   R Documentation

_E_x_p_o_n_e_n_t_i_a_l _d_e_c_a_y _m_o_d_e_l

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

     Exponential decay model with or without a nonzero lower limit.

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

       EXD.2(fixed = c(NA, NA), names = c("d", "e"), ...)

       EXD.3(fixed = c(NA, NA, NA), names = c("c", "d", "e"), ...)

_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: vector of character strings giving the names of the
          parameters (should not contain ":"). The default parameter
          names are: init, plateau, k.

     ...: additional arguments to be passed from the convenience
          functions.

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

     The exponential decay model is a three-parameter model with mean
     function:


                     f(x) = c + (d-c)(exp(-x/e))


     The parameter init is the upper limit (attained at x=0), the
     parameter plateau is the lower limit  reached for x going to
     infinity and the parameter e>0 is determining the steepness of the
      decay. The curve is monotonously decreasing in x.

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

     A list of class 'drcMean', containing the mean function, the self
     starter function, the parameter names and other components such as
     derivatives and a function for calculating ED values.

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

     Christian Ritz

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

     Organisation for Economic Co-operation and Development (OECD)
     (2006) _Current approaches in the statistical analysis of
     ecotoxicity data: A guidance to application - annexes_, Paris:
     OECD (p. 80).

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

     Similar models giving exponential increasing curves are 'AR.2' and
     'AR.3'.

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

     ## Fitting an exponential decay model
     ryegrass.m1<-drm(rootl~conc, data=ryegrass, fct=EXD.3())

     plot(ryegrass.m1)

     summary(ryegrass.m1)

