

Ratkowsky2(NISTnls)                          R Documentation

_P_a_s_t_u_r_e _y_i_e_l_d _d_a_t_a

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

     The `Ratkowsky2' data frame has 9 rows and 2 columns.

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

       y: A numeric vector of pasture yields.

       x: A numeric vector of growing times.

_F_o_r_m_a_t_:

     This data frame contains the following columns:

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

     This model and data are an example of fitting sigmoidal
     growth curves taken from Ratkowsky (1983).  The
     response variable is pasture yield, and the predictor
     variable is growing time.

_S_o_u_r_c_e_:

     Ratkowsky, D.A. (1983).  Nonlinear Regression Modeling.
     New York, NY:  Marcel Dekker, pp. 61 and 88.

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

     library(NISTnls)
     data(Ratkowsky2)
     plot(y ~ x, data = Ratkowsky2)
     fm1 <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
                start = c(b1 = 100, b2 = 1, b3 = 0.1), warnOnly = TRUE)
     fm2 <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
                start = c(b1 = 75, b2 = 2.5, b3 = 0.07), warnOnly = TRUE)
     fm3 <- nls(y ~ 1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
                start = c(b2 = 1, b3 = 0.1), warnOnly = TRUE, alg = "plinear")
     fm4 <- nls(y ~ 1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
                start = c(b2 = 2.5, b3 = 0.07), warnOnly = TRUE, alg = "plinear")
     ## Using a self-starting model
     fm5 <- nls(y ~ SSlogis(x, Asym, xmid, scal), data = Ratkowsky2)
     fm5

