This function computes Engle's ARCH test. The null hypothesis of this Lagrange Multiplier test is that a series of residuals exhibits no ARCH effects. The alternative hypothesis is that ARCH(lag) effects are present. The lag is specified by the User.
numeric, suspected order of ARCH process, if not specified lag=1 is taken
References
Engle, R. F., 1982. Autoregressive conditional heteroscedasticity with estimates of the variance of United Kingdom inflation. Econometrica50, 987--1007.