Let \(\epsilon _i\), \(1\leq i\leq n\), be independent identically distributed normal \(N(0,\sigma ^2)\) random variables and consider the model \[ y_i=i\alpha +\gamma i^2+\epsilon _i,\qquad 1\leq i\leq n. \] We observe \(y_i\), \(1\leq i\leq n\).
(a) Find the maximum likelihood estimators for \(\alpha \), \(\gamma \), and \(\sigma ^2\).
(b) Compute the joint distribution of the maximum likelihood estimators for \((\alpha ,\gamma )\).