Formula_22996

\[\begin{gathered}\varphi_{t_{1}, \ldots, t_{n}}\left(u_{1}, \ldots, u_{n}\right)= \\=\exp \left\{i \sum_{k=1}^{n} A\left(t_{k}\right) u_{k}-\frac{1}{2} \sum_{k, j=1}^{n} B\left(t_{k}, t_{j}\right) u_{k} u_{j}\right\},\end{gathered}\]