R/test_symmetry.R

In xnet: Two-Step Kernel Ridge Regression for Network Predictions

#' test the symmetry of a matrix
#'
#' This function tells you whether a matrix is symmetric,
#' skewed symmetric, or not symmetric. It's used by \code{\link{tskrr}}
#' to determine which kind of homologous network is represented by
#' the label matrix.
#'
#' @param x a matrix
#' @param tol a single numeric value with the tolerance for comparison
#'
#' @return a character value with the possible values "symmetric",
#' "skewed" or "none".
#'
#' @seealso \code{\link{tskrrHomogeneous}} for
#' more information on the values for the slot \code{symmetry}
#'
#' @examples
#' mat1 <- matrix(c(1,0,0,1),ncol = 2)
#' test_symmetry(mat1)
#' mat2 <- matrix(c(1,0,0,-1), ncol = 2)
#' test_symmetry(mat2)
#' mat3 <- matrix(1:4, ncol = 2)
#' test_symmetry(mat3)
#'
#' @export
test_symmetry <- function(x, tol = .Machine$double.eps){
  if(!is.matrix(x))
    stop("x should be a matrix")
  idl <- lower.tri(x)
  tx <- t(x)

  if(all(abs(x[idl] - tx[idl]) < tol )){
    out <- "symmetric"
  } else if(all( abs(x[idl] + tx[idl]) < tol )){
    out <- "skewed"
  } else {
    out <- "none"
  }
  return(out)
}