R/selectsys.R

In benubah/control: A Control Systems Toolbox

#' @title Select/Remove Subsystem in State-space Model
#'
#' @aliases removesys
#'
#' @usage selectsys(statesys, inputs, outputs, states)
#'        removesys(statesys, inputs, outputs, states)
#'
#'
#' @description
#' \code{selectsys} extracts a subsystem from a larger state-space system.
#' \code{removesys} removes specified inputs, outputs, and state from a state-space system.
#'
#'
#' @details
#' \code{subsys <- selectsys(statesys,inputs,outputs)} will extract a state
#' space subsystem with the specified inputs and outputs.
#'
#' \code{subsys <- selectsys(statesys, inputs,outputs,states)} will return
#' the state space subsystem with the specified inputs, outputs, and states.
#'
#' \code{subsys <-  removesys(statesys, inputs, outputs)} will remove the specified inputs and outputs from the system.
#'
#' \code{subsys <-  removesys(statesys, inputs, outputs, states)} will
#' also return a state-space model with the specified inputs, outputs, and
#' states removed from the system.
#'
#' @param statesys   LTI system model of state-space model
#' @param inputs single integer or vector specifying the particular inputs to be selected/removed
#' @param outputs single integer or vector specifying the particular outputs to be selected/removed
#' @param states single integer or vector specifying the particular states to be selected/removed
#'
#' @return Returns a subsystem of the state-space model
#'
#' @seealso \code{\link{append}}
#'
#' @examples
#' A <- rbind(c(33,2,5), c(23,200,2), c(9,2,45))
#' B <- rbind(c(4,5), c(12,5), c(82,1))
#' C <- rbind(c(34,56,2), c(6,2,112))
#' D <- rbind(c(2,0), c(0,19))
#' sys1 <- ss(A, B, C, D)
#'  selectsys(sys1, 1, 1) # extract subsystem for only input 1 and output 1
#'  selectsys(sys1, 2,2) # extract subsystem for only input 2 and output 2
#'  selectsys(sys1, 2, 1:2) # extract subsystem for only input 1 and output 1 to 2
#'  selectsys(sys1, 1:2, 2) # extract subsystem for only input 1 to 2 and output 2 to 2
#'  selectsys(sys1, 2, 2, 1:2) # extract subsystem for only input 2 and output 2 but states 1 to 2
#'  removesys(sys1, 1,2) # removes input 1 and output 2
#' @export
selectsys <- function(statesys, inputs, outputs, states) {
  errmsg <- abcdchk(statesys)
  if (errmsg != "") {
    stop("selectsys: " + errmsg)
  }
  a <- statesys[[1]]
  b <- statesys[[2]]
  c <- statesys[[3]]
  d <- statesys[[4]]

  if (nargs() == 3) {
    stateselect <- 1:nrow(a)
  }
  if (nargs() == 4) {
       stateselect <- states
  }
  if (!is.null(a)) {
     a_extracted <- a[stateselect, stateselect]
  } else {
     a_extracted <- c()
    }
  if (!is.null(b)) {
     b_extracted <- b[stateselect, inputs, drop = FALSE]
  }  else {
     b_extracted <- c()
  }
  if (!is.null(c)) {
     c_extracted <- c[outputs, stateselect, drop = FALSE]
  }  else {
     c_extracted <- c()
  }
  if (!is.null(d)) {
     d_extracted <- d[outputs, inputs, drop = FALSE]
  }  else {
     d_extracted <- c()
  }

  return(ss(a_extracted, b_extracted, c_extracted, d_extracted))
}