regr_param_ex: Computes extended set of regression parameters: R2ex
In conmolfields: Continuous molecular fields

Computes extended set of regression parameters: R2ex

1	regr_param_ex(predval, expval, trainval)

`predval`
`expval`
`trainval`

##---- Should be DIRECTLY executable !! ----
##-- ==>  Define data, use random,
##--	or do  help(data=index)  for the standard data sets.

## The function is currently defined as
regr_param_ex <- function(predval, expval, trainval) {
  n_p <- length(predval)
  rss <- 0
  for (i in 1:n_p) {
    rss <- rss + (predval[i] - expval[i]) * (predval[i] - expval[i])
  }
  r2ex <- 1 - ((rss/(n_p-1)) / var(trainval))
  r2ex
}