请问R中的TVECM(data, lag = 1, nthresh = 1, trim = 0.05,    ngridBeta = 50, ngridTh = 50, plot = TRUE,    th1 = list(exact = NULL, int = c("from", "to"), around = "val"),    th2 = list(exact = NULL, int = c("from", "to"), around = "val"),    beta = list(exact = NULL, int = c("from", "to"), around = c("val", "by")),    restr = c("none", "equal", "signOp"),    common = c("All", "only_ECT"),    include = c("const", "trend", "none", "both"),    dummyToBothRegimes = TRUE, beta0 = 0,    methodMapply = FALSE, trace = TRUE)函数中，门限变量是如何选定的？是data中两列数据的误差修正项（EG协整第一步的残差）还是直接做差所得？另外门限变量的滞后阶数是默认滞后一阶吗？求解答！！