Characteristic function of a random vector
= Characteristic function of a random vector
{title2=$\varphi_X(u)=\mathbb E[e^{i\langle u,X\rangle}]$}
For an $\mathbb R^d$-valued random vector, the characteristic function is $\varphi_X(u)=\mathbb E[e^{i\langle u,X\rangle}]$. It determines the joint distribution and satisfies $\varphi_{AX}(u)=\varphi_X(A^Tu)$ for every deterministic matrix $A$.