Optional ReadonlydistReadonlyendsTrain-end indices: each fit sees returns[0 … end].
Optional ReadonlyexogenousGARCH-X: x aligned with the returns (garch and gjr); see FitOptions.exogenous. Forecasts hold it at its last value.
Optional ReadonlymeanA fitted constant (default) or zero; see FitOptions.mean.
Optional ReadonlymodelReadonlyreturnsOptional ReadonlytargetVariance targeting (garch and gjr); see FitOptions.targetVariance.
fitsAt's question: the returns and the train ends to fit at.