ิby computing the sample ACF and sample PACF of the residuals
to see whether they do not form any pattern and are
statistically insignificant, and by doing a Portmanteau test of
the residuals – the more accurate is the Ljung–Box test [25].
The Ljung–Box test tests whether the first k autocorrelations of
the residuals are significantly different from what would be
expected from a white noise process.