PsiGARCH11(mean,volatility,err_coef,ar_coef,val0, stdev0)

where a1 ≥ 0, b1 ≥ 0, at least one of a1 or b1 must be positive and ω > 0 

PsiGARCH11 generates a generalized first order autoregressive conditional heteroskedasticity process with mean mean, volatility volatility, error coefficient err_coef, autoregressive coefficient ar_coef, value at time 0 val0 and initial standard deviation stdev0. 

PsiGARCH11 is a generalization of PsiARCH1 where the conditional variance at time t is a weighted combination of  volatility, the preceeding squared deviation of the mean and the prior variance. 

For more information, see the Analytic Solver Reference Guide downloadable from Analytic Solver by clicking Help -- User Guides -- Analytic Solver Reference Guide.