R/L2E_isotonic.R

In jocelynchi/L2E-package-demo: Robust Structured Regression via the L2 Criterion

#' L2E isotonic regression
#'
#' \code{L2E_isotonic} performs isotonic regression under the L2 criterion. Available methods include proximal gradient descent (PG) and majorization-minimization (MM).
#'
#' @param y Response vector
#' @param beta Initial vector of regression coefficients
#' @param tau Initial precision estimate
#' @param method Available methods include PG and MM. MM by default.
#' @param max_iter Maximum number of iterations
#' @param tol Relative tolerance
#' @param Show.Time Report the computing time
#' @return Returns a list object containing the estimates for beta (vector) and tau (scalar),
#' the number of outer block descent iterations until convergence (scalar),
#' and the number of inner iterations per outer iteration for updating beta (vector) and tau or eta (vector)
#' @export
#' @examples
#' set.seed(12345)
#' n <- 200
#' tau <- 1
#' x <- seq(-2.5, 2.5, length.out=n)
#' f <- x^3
#' y <- f + (1/tau) * rnorm(n)
#'
#' ## Clean Data
#' plot(x, y, pch=16, cex.lab=1.5, cex.axis=1.5, cex.sub=1.5, col='gray')
#' lines(x, f, lwd=3)
#'
#' tau <- 1
#' b <- y
#' ## Least Squares method
#' iso <- isotone::gpava(1:n, y)$x
#' ## MM method
#' sol_mm <- L2E_isotonic(y, b, tau)
#' ## PG method
#' sol_pg <- L2E_isotonic(y, b, tau, method='PG')
#'
#' plot(x, y, pch=16, cex.lab=1.5, cex.axis=1.5, cex.sub=1.5, col='gray')
#' lines(x, f, lwd=3)
#' lines(x, iso, col='blue', lwd=3) ## LS
#' lines(x, sol_mm$beta, col='red', lwd=3) ## MM
#' lines(x, sol_pg$beta, col='dark green', lwd=3) ## PG
#'
#' ## Contaminated Data
#' ix <- 0:9
#' y[45 + ix] <- 14 + rnorm(10)
#'
#' plot(x, y, pch=16, cex.lab=1.5, cex.axis=1.5, cex.sub=1.5, col='gray')
#' lines(x, f, lwd=3)
#'
#' tau <- 1
#' b <- y
#' iso <- isotone::gpava(1:n, y)$x
#' sol_mm <- L2E_isotonic(y, b, tau)
#' sol_pg <- L2E_isotonic(y, b, tau, method='PG')
#'
#' plot(x, y, pch=16, cex.lab=1.5, cex.axis=1.5, cex.sub=1.5, col='gray')
#' lines(x, f, lwd=3)
#' lines(x, iso, col='blue', lwd=3) ## LS
#' lines(x, sol_mm$beta, col='red', lwd=3) ## MM
#' lines(x, sol_pg$beta, col='dark green', lwd=3) ## PG
#'
L2E_isotonic <- function(y, beta, tau, method = "MM", max_iter = 1e2, tol = 1e-4, Show.Time = TRUE) {

  if (tau <= 0) stop("Entered non-positive initial tau")

  if (method == "MM") {
    l2e_regression_isotonic_MM(y=y, beta=beta, tau=tau, max_iter=max_iter, tol=tol, Show.Time=Show.Time)
  }
  else if (method == "PG") {
    l2e_regression_isotonic(y=y, b=beta, tau=tau, max_iter=max_iter, tol=tol, Show.Time=Show.Time)
  }
  else {
    stop("Method unavailable. Available methods are PG and MM.")
  }
}