GARCH model variance calculation

I have a financial return series, i would like to estimate volatitlity through a GARCH(1,1), my task is not to correct heteroskedasticty in residuals; but only to estimate volatility, i used command garch('Offset','NaN','GARCHLags',1,'ARCHLags',1).I used the equation variance=constant+GARCH coef*variance(-1)+ARCHcoef-r²(-1). This is a right way to do it?