Formula

Enter an expression in the S-PLUS language specifying the nonlinear regression model. The variables used in the formula are the columns of the data set, the parameters to be estimated, and S-PLUS functions. The response variable appears first, followed by a tilde "~", and then the function to be minimized. For example:

y ~ b0 * exp(b1 * x)

The right hand side of the formula could also be a selfStarting function, that is a function with another function as an attribute that provides initial estimates for its parameters. See the help file for the function nls for a list of available self-starting functions in S-PLUS.