regr_param: Computes regression parameters: R2, RMSE, RMSE_pc, MAE
In conmolfields: Continuous molecular fields

Computes regression parameters: R2, RMSE, RMSE_pc, MAE

1	regr_param(predval, expval)

`predval`
`expval`

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

## The function is currently defined as
function (predval, expval) 
{
    n <- length(predval)
    expval_mean <- mean(expval)
    ss <- var(expval) * (n - 1)
    rss <- 0
    rsa <- 0
    for (i in 1:n) {
        rss <- rss + (predval[i] - expval[i]) * (predval[i] - 
            expval[i])
        rsa <- rsa + abs(predval[i] - expval[i])
    }
    r2 <- (ss - rss)/ss
    rmse <- sqrt(rss/n)
    mae <- rsa/n
    list(R2 = r2, RMSE = rmse, MAE = mae)
  }