Index exceeds the number of array elements (1)

Hello,

I'm implementing NMPC for the control of quadcopter. minimal_example is the script which calls nmpc. u is the control vector of 4 variables, x is a state vector of 12 variables. Dynamic equations (second order system) are described in mathmodel function. During the simulation it shows the error:

Index exceeds the number of array elements (1).

Error in minimal_example>mathmodel (line 82)

xdot = [x(2);

Can anyone suggest how can I fix it? Thank you in advance!

function xdot = mathmodel(t, p, x, u, T)
    
xdot = [x(2);
    (x(4)*x(6)*(p.Iyy-p.Izz)-(u(1)+u(2)+u(3)+u(4))*p.IR*x(4)...
    +(p.b*p.l*(u(2)^2-u(4)^2)))/p.Ixx; %phi_dot
    x(4);    %theta
    (x(2)*x(6)*(p.Izz-p.Ixx)+(u(1)+u(2)+u(3)+u(4))*p.IR*x(2)...
    +(p.b*p.l*(u(3)^2-u(1)^2)))/p.Iyy; %theta_dot
    x(6); %ksi
    (x(4)*x(2)*(p.Ixx-p.Iyy)+(p.d*(u(1)^2+u(3)^2-u(2)^2-u(4)^2)))/p.Izz; %ksi_dot
    x(8); %X
    ((p.b*(u(1)^2+u(2)^2+u(3)^2+u(4)^2))*(sin(x(1))*sin(x(5))...
    +cos(x(1))*sin(x(3))*cos(x(5))))/p.mass; %X_dot
    x(10); %Y
    ((p.b*(u(1)^2+u(2)^2+u(3)^2+u(4)^2))*(cos(x(1))*sin(x(3))*sin(x(5))...
    -sin(x(1))*cos(x(5))))/p.mass; %Y_dot
    x(12); %Z
    ((p.b*(u(1)^2+u(2)^2+u(3)^2+u(4)^2))*(cos(x(1))*cos(x(3)))-p.mass*p.g)/p.mass]'; %Z_dot
end

Answer 1

[Jim Riggs]

In the calculation of xdot I see subscripted references for x (up to 12) and u (up to 4).

You should check the size of x and u in the function that is calling "mathmodel" and make sure that x and u have the propper dimensions -> x(12) and u(4)

[pozmogov]

Thank you for the answer! The problem has been solved by specifying the tolerances of the ODE solver and by proper setting the xmeasure and u dimencions (row/column vector)

 tol_opt = 1e-6;
        opt_option = 0;
        type = 'differential equation';
        atol_ode_real = 1e-8;
        rtol_ode_real = 1e-8;
        atol_ode_sim = atol_ode_real;
        rtol_ode_sim = rtol