PsiARCH1(mean, volatility, err_coef, val0)
where a1 > 0 must be true for stationarity.
PsiARCH1 generates a first order autoregressive conditional heteroskedasticity process with mean mean, volatility volatility, error coefficient err_coef and time value at time 0 val0.
PsiARCH1 should be used when it can be assumed that the variance of the time series will fluctuate throughout time.
For more information, see the Analytic Solver Reference Guide downloadable from Analytic Solver by clicking Help -- User Guides -- Analytic Solver Reference Guide.