Error while debugging the customized simscape component

Hello, I'm using Simscape language to make a customized component. Here is the code:

%----------------------------------------------------

component Plant
%%Physical model

nodes
  T = foundation.mechanical.translational.translational; %T:right 
  R = foundation.mechanical.rotational.rotational; % R:right
end

parameters
  m = { 2.0, 'kg' }; % Mass of the robot
  J = {0.15625,  'kg*m^2'  }; %Moment of inertia
  rw = {0.1, 'm'}; % Wheel radius
  Wd = {0.4, 'm'}; % Chassis width between wheels
  init_s = {0, 'm'}; % Intial distance,s
  init_theta = {0, 'rad'}; % Initial orientation,theta 
 end

variables
  v = { 0, 'm/s' };   %%translational velocity
  w = { 0, 'rad/s' };  %rotational velocity
  fl = {0,'kg*m/s^2'};       % force left 
  fr = {0,'kg*m/s^2'};       % force right or kg*m/s^2
  theta = {0,'rad'}; % orientation
  s = {0, 'm'};       % distance of the path between 2 points    
end

function setup
  across( v, T.v, []);
  across( w, R.w, [] );
  through(fr, T.f, [] );
  through(fl, T.f, [] );
  theta = init_theta;
  s = init_s;
end

equations 
  v == s.der;
  w == theta.der; 
   v.der == (fr + fl)/m;    
   w.der == (fr - fl)*rw/J;
end
end
%---------------------------------------------------
It seems OK when I build the component without any error but when I compose the component in Simulink environment, the error appears to be like:
-------------------------------------------------------------
Nonlinear solver: Linear Algebra error. Failed to solve using iteration matrix.
Initial conditions solve failed to converge.
Dependency found among topology equations. Check for missing reference node. 
-------------------------------------------------------------
Any advice?
Regards,
Azizi

Answer 1

[Sabin]

This error points to a missing reference node. Each topologically distinct circuit within a domain must contain at least one reference block.