RLC_func=@(om,R,L,C) [...
-1,1,1,0,0; ...
0,1,0,-1,1; ...
(1j*om*L(1)+1/(1j*om*C(1))),0,0,(1j*om*L(2)),0; ...
0,0,0,(1j*om*L(2)),(1/(1j*om*C(2))); ...
0,0,(1j*om*L(3)+1/(1j*om*C(3))+R(3)),0,(1/(1j*om*C(2)))];

u=1;
R=[nan,nan,1];
L=[1,1,1];
C=[1,1,1];
om_v=logspace(-1,1,201);

U=[0,0,u,0,0].';
I=zeros(5,201);

for k=1:numel(om_v)
    om=om_v(k);
    M=RLC_func(om,R,L,C);
    I(:,k)=(M\U);
end

theta=angle(I(3,:));
I3_Am=abs(I(3,:));

figure
subplot(2,1,1);
semilogx(om_v,I3_Am,'-b')
title('Amplitude')
xlabel('\Omega')
ylabel('|i_3|')
subplot(2,1,2)
semilogx(om_v,theta,'-b')
title('Phase')
xlabel('\Omega')
ylabel('\Theta')
ylim([-pi pi])