Ratkowsky2              package: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.

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

     This data frame contains the following columns:

     _y A numeric vector of pasture yields.

     _x A numeric vector of growing times.


_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:

     Try <- function(expr) if (!inherits(val <- try(expr), "try-error")) val
     plot(y ~ x, data = Ratkowsky2)

     Try(fm1 <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
                start = c(b1 = 100, b2 = 1, b3 = 0.1)))
     Try(fm1a <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2,
                 trace = TRUE, alg = "port", 
                 start = c(b1 = 100, b2 = 1, b3 = 0.1)))
     Try(fm2 <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
                start = c(b1 = 75, b2 = 2.5, b3 = 0.07)))
     Try(fm2a <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2,
                 trace = TRUE, alg = "port", 
                 start = c(b1 = 75, b2 = 2.5, b3 = 0.07)))
     Try(fm3 <- nls(y ~ 1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
                start = c(b2 = 1, b3 = 0.1), alg = "plinear"))
     Try(fm4 <- nls(y ~ 1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
                start = c(b2 = 2.5, b3 = 0.07), alg = "plinear"))

     ## Using a self-starting model
     Try(fm5 <- nls(y ~ SSlogis(x, Asym, xmid, scal), data = Ratkowsky2))
     summary(fm5)

