s_function 2dof

Hello!!!!

l try to use s_function in simulink and I get this error:

Error in 'BRAS_2DOF/S-Function1' while executing MATLAB S-function 'Dynamique2DOF', flag = 0 (initialize), at start of simulation.

Caused by:

Subscript indices must either be real positive integers or logicals.

this is my code in joint piece

Answer 1

[ag]

Hi James,

The error message that you are facing is caused by the below line:

M = [m1*lc1^2+m2(l1^2+lc2^2+2*l1+lc2*cos(q2))+I1+I2, m2(lc2^2+l1*lc2*cos(q2));m2lc2^2+l1*lc2*cos(q2)+I2, m2lc2^2+I2];

As m2 is defined as a scalar in the script, using indexing in the following way "m2(l1^2+lc2^2+2*l1+lc2*cos(q2))" is not supported.

There are a few more syntax errors that I obsereved in the code provided. Below is the code after correcting the syntax errors with the comments explaining the changes.

function[sys,x0,str,ts] = Dynamique2DOF(t,x,u,flag)
    m1=9.5; m2=5;
    l1=0.25; l2=0.16;
    lc1=0.20;lc2=0.14;
    I1=4.3*10^(-3); I2=6.1*10^(-3); 
    g=9.8;
    q2=1;

    %providing a temporary definition for M, C and G 
    M = [1, 2; 3, 4]
    C = [1, 2; 3, 4]
    G = [1, 2; 3, 4]
    %M = [m1*lc1^2+m2(l1^2+lc2^2+2*l1+lc2*cos(q2))+I1+I2, m2(lc2^2+l1*lc2*cos(q2));m2lc2^2+l1*lc2*cos(q2)+I2, m2lc2^2+I2];
    %to avoid the error "Subscript indices must either be real positive integers or logicals."
    
    %C = [-m2*l1*lc2*sin(q2)*dq2, -m2*l1*lc2*sin(q2)*(dq1+dq2); m2*l1*lc2*sin(q2)*dq2, 0];
    %dq2 is undefined
    
    %G = [(m1*lc1+m2*l1)*g*cos(q1)+m2*lc2*g*cos(q1+q2); m2*lc2*g*cos(q1+q2)];
    %q1 is undefined

    sys = 0, x0 = 0, str = 0, ts = 0; %these variables must be initialized irrespective of the "flag", as these are returned by the function "Dynamique2DOF"
    
    switch flag %comma is not allowed here
        case 0          
            [sys,x0,str,ts]=mdlInitializeSizes;
        case 1
            sys = mdlDerivatives(t,x,u);
        case 3
            sys = mdlOutputs(t,x,u);
        case { 2, 4, 9 }
            sys = [];
        otherwise
            error(['Unhandled flag = ',num2str(flag)]);
        end
end %ending a function is necessary

function [sys,x0,str,ts]=mdlInitializeSizes
    sizes = simsizes;
    sizes.NumContStates  = 2; 
    sizes.NumDiscStates  = 0;
    sizes.NumOutputs     = 4;
    sizes.NumInputs      = 2;
    sizes.DirFeedthrough = 0;
    sizes.NumSampleTimes = 1;
    sys=simsizes(sizes);
    x0=[1 0.8 0 0];
    str=[];
    ts=[1 0];
end %ending a function is necessary

function sys=mdlDerivatives(t,x,u) %semicolon is not allowed here
    dq1 = q2;
    dq2 = (tau - C*dq2 + G)/M;
    
    sys(1)=dq1;
    sys(2)=dq2;
    sys(3)=ddq1;
    sys(4)=ddq2;
end %ending a function is necessary
    
function sys=mdlOutputs(t,x,u)
    sys(1)=q1;
    sys(2)=q2;
    sys(3)=q3;
    sys(4)=q4;
end %ending a function is necessary

Hope this helps!

[Walter Roberson]

MATLAB does not support implied multiplication at all. m2(expression) is treated as an indexing request, not as a multiplication request.