#' Tensor Times Matrix (n-mode tensor matrix product)
#'
#' @param T array of order at least \code{mode}
#' @param M matrix, the right hand side of the mode product such that
#'  \code{ncol(M)} equals \code{dim(T)[mode]}
#' @param mode the mode of the product in the range \code{1:length(dim(T))}
#'
#' @returns multi-dimensional array of the same order as \code{T} with
#'  \code{mode} dimension equal to \code{nrow(M)}
#'
#' @export
ttm <- function(T, M, mode = length(dim(T))) {
    storage.mode(T) <- storage.mode(M) <- "double"
    .Call("C_ttm", T, M, as.integer(mode))
}

#' @rdname ttm
#' @export
`%x_1%` <- function(T, M) ttm(T, M, 1L)
#' @rdname ttm
#' @export
`%x_2%` <- function(T, M) ttm(T, M, 2L)
#' @rdname ttm
#' @export
`%x_3%` <- function(T, M) ttm(T, M, 3L)
#' @rdname ttm
#' @export
`%x_4%` <- function(T, M) ttm(T, M, 4L)