R/genInit.R

In netSEM: Network Structural Equation Modeling

##' Generate multiple initial vectors for the nls function in netSEM().
##'
##' Currently the non-linearizable function included in netSEM() is y = a + b * exp(c * x), where a, b and c are coefficients to be estimated. 
##' Thus an initial vector contains three values. 
##' The random initial values are generated by a uniform distribution between the bounds.
##'
##' @title Generate initial values for nls function
##' @param bounds a list of three vectors of length = 2. 
##' Each vector gives the upper and lower limits of an interval from which the initial values are randomly generated. 
##' The default values list(a1 = c(-3, 3), a2 = c(-3, 3), a3 = c(-3, 3)) sets limits of all three initial values to be (-3, 3).
##' @param k a positive integer (default = 50). The number of initial vectors to generate.
##' @export
##'
##' @return a data frame. Each column corresponds to a coefficient. Each row corresponds to a random initial vector.
##' 
##'
##' @examples
##' genInit(list(a1 = c(0,2), a2 = c(4,5), a3 = c(-1, -0.5)), k = 20 )
genInit <- function(bounds = list(a1 = c(-3, 3),
                                  a2 = c(-3, 3),
                                  a3 = c(-3, 3)),
                    k = 50)
{
  ans <- sapply(bounds, FUN = function(x) {
    runif(k, x[-2], x[2])
  })
  return(as.data.frame(ans))
}