block does not fully set the dimensions of output 'ddtheta'

Hello

I am trying to control dimming for 2 dof system, here is my problem:

Error:Block ''untitled/Subsystem/MATLAB Function'' does not fully set the dimensions of output 'ddtheta'.

Does anyone know how to fix this?

Here is my sctructure:

Here is code inside MATLAB function:

function ddtheta = Robot_2_DOF(dtheta,theta,to)
m1=1;
m2=1;
l1=1;
l2=1;
g=9.81;

theta1=theta(1);
theta2=theta(2);
dtheta1=dtheta(1);
dtheta2=dtheta(2);
%% M
M=[((m1+m2)*l1^2+m2*l2^2+2*m2*l1*l2*cos(theta2))  m2*l2^2+m2*l1*l2*cos(theta2) ;...
   m2*l2^2+m2*l1*l2*cos(theta2)                   m2*l2^2                     ];
%% V
V=[-l1*l2*m2*sin(theta2)*(2*dtheta1*dtheta2^2) ;...
    m2*l1*l2*dtheta1^2*sin(theta2)];
%% G
G=[(m1+m2)*g*l1*cos(theta1)+m2*g*l2*cos(theta2) ;...
    m2*g*l2*cos(theta1+theta2)];
%% ddtheta
ddtheta=M/(to-V-G-dtheta);

Answer 1

[Sam Chak]

Hi @Peter

I'm not familiar with the specifics of your Robot dynamics, but based on my understanding of MATLAB, it seems that you should use a backslash operator (\) instead of a forward slash operator (/).

tspan   = [0 2];
theta0  = [1 0];
[t, x]  = ode45(@(t, theta) Robot_2_DOF(t, theta, 1), tspan, theta0);
plot(t, x), grid on

function ddtheta = Robot_2_DOF(t, theta, to)
    m1  = 1;
    m2  = 1;
    l1  = 1;
    l2  = 1;
    g   = 9.81;
    
    theta1  = theta(1);
    theta2  = theta(2);
    dtheta1 = theta1;
    dtheta2 = theta2;
    
    %% M
    M   = [((m1+m2)*l1^2+m2*l2^2+2*m2*l1*l2*cos(theta2))  m2*l2^2+m2*l1*l2*cos(theta2) ;...
           m2*l2^2+m2*l1*l2*cos(theta2)                   m2*l2^2                     ];
    
    %% V
    V   = [-l1*l2*m2*sin(theta2)*(2*dtheta1*dtheta2^2) ;...
           m2*l1*l2*dtheta1^2*sin(theta2)];
    
    %% G
    G   = [(m1+m2)*g*l1*cos(theta1)+m2*g*l2*cos(theta2) ;...
            m2*g*l2*cos(theta1+theta2)];
    
    %% ddtheta
    ddtheta = M\(to - V - G - [dtheta1; dtheta2]);  % <--- use backslash \
end

[Peter]

Hi @Sam Chak

I tried doing what you said, I tried changing a backslash operator (\) instead of a forward slash operator (/), but it still doesn't seem to solve the error. If you have any other solution, please let me know. I'm really grateful and waiting for your response.

[Sam Chak]

Hi @Peter

I don't have any issue running the corrected code (backslash) below. Are you sure that you are still getting the same Error: Block "MATLAB Function" does not fully set the dimensions of output 'ddtheta'? If that happens, most probably the initial values in your Integrator blocks are incorrectly set.

function ddtheta = Robot_2_DOF(theta, dtheta, to)

m1 = 1;

m2 = 1;

l1 = 1;

l2 = 1;

g = 9.81;

theta1 = theta(1);

theta2 = theta(2);

dtheta1 = dtheta(1);

dtheta2 = dtheta(2);

%% M

M = [((m1+m2)*l1^2+m2*l2^2+2*m2*l1*l2*cos(theta2)) m2*l2^2+m2*l1*l2*cos(theta2) ;...

m2*l2^2+m2*l1*l2*cos(theta2) m2*l2^2 ];

%% V

V = [-l1*l2*m2*sin(theta2)*(2*dtheta1*dtheta2^2) ;...

m2*l1*l2*dtheta1^2*sin(theta2)];

%% G

G = [(m1+m2)*g*l1*cos(theta1)+m2*g*l2*cos(theta2) ;...

m2*g*l2*cos(theta1+theta2)];

%% ddtheta

ddtheta = M\(to - V - G - dtheta);

end