R/fun.N_3.R

In GMDHreg: Regression using GMDH Algorithms

#' @title GMDH MIA auxiliar functions
#'
#' @description Performs auxiliar tasks to predict.mia
#'
#' @keywords internal
#'
fun.N_3 <- function(x, y) {

  nombres <- colnames(x)
  resultado <- vector(mode = "list", length = 2)
  names(resultado) <- c("coef", "CV")
  tol <- sqrt(.Machine$double.eps)

  x <- cbind(1, x[, 1], x[, 2],
             I(x[, 1]^2), I(x[, 2]^2),
             x[, 1] * x[, 2])

  Xsvd <- svd(x)
  D <- diag(1 / Xsvd$d)
  D[D <= tol] <- 0
  XtX_inv <- Xsvd$v %*% D %*% D %*% t(Xsvd$v)
  C <- XtX_inv %*% crossprod(x, y)
  rownames(C) <- c("Ind", nombres, paste0(nombres, "^2", sep = ""), "interac")

  RSS <- sum((x %*% C - y)^2)
  n <- nrow(x)
  sigma2 <- RSS / n
  rank <- ncol(x)
  k <- rank + 1

  logL <- -(n / 2) * (log(RSS / n)) - (n / 2) * (log(2 * pi)) - (n / 2)
  covmat <- sigma2 * XtX_inv

  lambdas <- eigen(covmat, only.values = TRUE)$values
  lambda_m <- mean(lambdas)
  complexity <- (1 / 2) / (lambda_m * lambda_m) * sum((lambdas - lambda_m)^2)
  CV <- -2 * logL + complexity
  CV <- round(CV, digits = 6)

  resultado$coef <- C
  resultado$CV <- CV
  class(resultado) <- "neurona"
  return(resultado)
}