# problem-12.8

problem-12.8 This model is actually done in the help page for the data set. We can fit the model by running the command

    > library(MASS)                 # load in help page
    > example(wtloss)
    > wtloss.fm
    Nonlinear regression model
      model:  Weight ~ b0 + b1 * 2^(-Days/th)
       data:  wtloss
        b0     b1     th
     81.37 102.68 141.91
     residual sum-of-squares:  39.24
    > plot(Weight ~ Days, wtloss)   # make scatterplot
    > lines(predict(wtloss.fm) ~ Days, data = wtloss)

The value of b0 is the predicted long-term weight. If we want the predicted amount after 365 days we have

    > predict(wtloss.fm, newdata=data.frame(Days=365))
    [1] 98.64

(Of course, predictions beyond the range of the data are not a good idea.)