How to convert a state-space model to transfer function?

Question

Following this question, I am trying to convert the state-space model from this tutorial back into its transfer-function form. I have tried the

R = 2.0;                % Ohms
L = 0.5;                % Henrys
Km = 0.1;               % torque constant
Kb = 0.1;               % back emf constant
Kf = 0.2;               % Nms
J = 0.02;               % kg.m^2/s^2
Td = 1;                 % models load disturbances

h1 = tf(Km, [L R]);            % armature
h2 = tf(1, [J Kf]);            % eqn of motion
dcm = ss(h2) * [h1 , Td];      % w = h2 * (h1 * Va + Td)

[b, a] = ss2tf(dcm.A, dcm.B, dcm.C, dcm.D);
dcm_tf = tf(b, a);

However, I get the error message:

IU must be specified for systems with more than one input.

Answer 1

According to this comment on Reddit, given the above system is Multiple-Input-Multiple-Output (MIMO), we need to specify the input index ni from the ss2tf()function. In this case the

[b, a] = ss2tf(dcm.A, dcm.B, dcm.C, dcm.D, 1);

returns the w / Va transfer function and the

[b, a] = ss2tf(dcm.A, dcm.B, dcm.C, dcm.D, 2);

returns the w / Td one.

Alternatively, one could simply use the tf(dcm) to convert the state-space model directly to transfer functions of both inputs.