Definition X:(Ω,F)→(Rd,Rd),X=(X1,X2,…,Xd) Column vector whose components are random variables X:(Ω,F)→(R,R). X(ω)=(X1,X2,…,Xd)(ω)=(X1(ω),X2(ω),…,Xd(ω))=(x1,x2,…,xd)