R/ss.R

In benubah/control: A Control Systems Toolbox

#' @title Create State-space Model.
#'
#' @description
#' \code{ss} creates the model for a system represented in state-space form
#'
#' @details
#' \code{ss} creates a model object for state-space systems.
#'
#'
#' @param A         An n x n matrix
#' @param B         An n x m matrix
#' @param C         An p x n matrix
#' @param D         An p x m matrix
#' @param Ts        Sample time for discrete time systems
#'
#' @return Returns a list object of 'ss' class.
#'
#' @seealso \code{\link{tf}} \code{\link{zpk}}
#'
#' @examples
#' A <- rbind(c(-2, -1), c(1,0))
#' B <- rbind(1,0)
#' C <- cbind(0,1)
#' D <- 0;
#' sys <- ss(A,B,C,D)
#'
#' \dontrun{  OR }
#'
#' sys <- ss(c(-2,-1,1,0), c(1,0), c(0,1), 0)
#'
#' \dontrun{  Access individual state-space sys elements as }
#'
#' sys$A
#' sys$B
#' sys$C
#' sys$D
#'
#' @export

ss <- function (A, B, C, D, Ts = NULL) {

        if ( is.vector(A) ) {
          A <- matrix(A, nrow = sqrt(length(A)), byrow = TRUE)
         }
            if ( is.vector(B) ) {
              B <- matrix(B, nrow = nrow(A))
             }
               if ( is.vector(C) ) {
                   C <- matrix(C, ncol = ncol(A))
               }
                  if ( is.vector(D) ) {
                      D <- matrix(D, ncol = ncol(B))
                   }

  response <- abcdchk(A,B,C,D);
  if (response != "") {
    err_msg <- paste("ss: ",response);
    stop(err_msg);
  }
  sys = list(A = A, B = B, C = C, D = D, Ts = Ts)
  class(sys) <- "ss"
  return(sys)
}

#' @export
print.ss <- function (x, ...) {
  # arg x is the same sys
  A <- x$A
  B <- x$B
  C <- x$C
  D <- x$D
  Ts <- x$Ts

  colnames(A) <- paste("x", 1:ncol(A), sep='')
  rownames(A) <- paste("x", 1:nrow(A), sep='')
  colnames(B) <- paste("u", 1:ncol(B), sep='')
  rownames(B) <- paste("x", 1:nrow(B), sep='')
  colnames(C) <- paste("x", 1:ncol(C), sep='')
  rownames(C) <- paste("y", 1:nrow(C), sep='')
  colnames(D) <- paste("u", 1:ncol(D), sep='')
  rownames(D) <- paste("y", 1:nrow(D), sep='')

  cat("\n", 'sys.A =', '\n\n')

  print(A, print.gap = 3, right = TRUE)
  cat("   \n")
  cat('sys.B =', '\n\n')
  print(B, print.gap = 3, right = TRUE)
  cat("   \n")
  cat('sys.C =', '\n\n')
  print(C, print.gap = 3, right = TRUE)
  cat("   \n")
  cat('sys.D =', '\n\n')
  print(D,print.gap = 3, right = TRUE)
  cat("   \n")

  if ( is.null(Ts) || Ts <= 0) {
    cat("\n State-Space system: Continuous time model", "\n")
  } else {
    cat("Sample Time =", Ts, "\n")
    cat("State-Space system: Discrete time model", "\n\n")
  }
}