[num,den]= series(num1,den1, num2,den2)

[a,b,c,d] = series(a1,b1,c1,d1,a2,b2,c2,d2, outputs1, inputs2)

[a,b,c,d] = series(a1,b1,c1,d1,a2,b2,c2,d2)

[num,den]= series(num1,den1, num2,den2, outputs1, inputs2)