#'
#' @param phi regression matrix, of size p*m
#' @param thresh threshold to say a cofficient is equal to zero
#'
#' @return a list with A, a matrix with relevant indices (size = p*m) and B, a
#'
#' @param phi regression matrix, of size p*m
#' @param thresh threshold to say a cofficient is equal to zero
#'
#' @return a list with A, a matrix with relevant indices (size = p*m) and B, a