Error calling ... This call-site expects more outputs than this function can supply. P-code function 'checkNonlinearInputs.p' produced an error.

Good evening,

I am currently working on a parallelipiped driving simulator with 3-DoF (heave, roll and pitch) that has 4 actuators on the corners, so I cannot use inverse kinematic to obtain the length of the four actuators (z1 is the rear right actuator, z2 front right and so on anti clockwise). So I decided to use Maple to write the kinematic solution (the varibles with subscript g) and the constraints, and to use a constrained minimization to find the length of actuators. However, if I use a single target to try the optimization(theta_t, phi_t, z_t), Simulink does not signal any error while using a trajectory of more points, Simulink gives me the following error "Error calling 'Opt/mycon'. This call-site expects more outputs than this function can supply. P-code function 'checkNonlinearInputs.p' produced an error.". I leave the code of the MATLAB function block below, which receives as input the two angles and the heave and has as output the four actuators length. How can I solve this problem to obtain a workink real-time optimization? Thanks in advance.

function [z1, z2, z3, z4] = Opt(theta_t, phi_t, z_t)
l = 0.82;
L = 1.6;
% theta_t = 1.5*pi/180;
% phi_t = 1.5*pi/180;
% z_t = 0.05;
%theta_g = atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2));
%phi_g = -atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l));
% x_g = ((-2*z(3) + 2*z(4))*z(1) + L^2)/(2*sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2));
% y_g = ((-z(3)^2 + (-2*z(1) + z(2) + z(4))*z(3) + l^2 + 2*z(1)*z(2) - z(2)*z(4))*L^2 + l^2*(z(3) - z(4))^2)/(2*sqrt(((L^2 + l^2)*z(3)^2 + (-2*L^2*z(2) - 2*l^2*z(4))*z(3) + (l^2 + z(2)^2)*L^2 + l^2*z(4)^2)/(l^2*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l);
% z_g = L*(z(2) + z(4))/(2*sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*sqrt(((L^2 + l^2)*z(3)^2 + (-2*L^2*z(2) - 2*l^2*z(4))*z(3) + (l^2 + z(2)^2)*L^2 + l^2*z(4)^2)/(l^2*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2))));
fun = @(z)120*(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)) - theta_t)^2 + 40*(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)) - phi_t)^2 ...
    + 1*(L*(z(2) + z(4))/(2*sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*sqrt(((L^2 + l^2)*z(3)^2 + (-2*L^2*z(2) - 2*l^2*z(4))*z(3) +1*(l^2 + z(2)^2)*L^2 + l^2*z(4)^2)/(l^2*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))) - z_t)^2;
lb = [0, 0, 0, 0];
ub = [0.1, 0.1, 0.1, 0.1];
if theta_t < 0.4*pi/180 
    options = optimoptions('fmincon','Display','iter','Algorithm','sqp', 'ConstraintTolerance', 1e-17, 'StepTolerance', 1e-10);
else
    options = optimoptions('fmincon','Display','iter','Algorithm','sqp', 'ConstraintTolerance', 1e-18, 'StepTolerance', 1e-10);
end
    function [c,ceq] = mycon(z)
        l = 0.82;
        L = 1.6;
        c = [atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)) - 3.5*pi/180; 
            -atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)) - 3.5*pi/180; 
            -atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)) - 2.5*pi/180; 
            -(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l))) - 2.5*pi/180];
        ceq = [-sin(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))*z(1) - 0.8000000000*cos(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2))) + ((-2*z(3) + 2*z(4))*z(1) + L^2)/(2*sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)); 
            -cos(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*cos(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))*z(2) - 0.8000000000*cos(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*sin(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2))) - 0.4100000000*sin(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l))) + L*(z(2) + z(4))/(2*sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*sqrt(((L^2 + l^2)*z(3)^2 + (-2*L^2*z(2) - 2*l^2*z(4))*z(3) + (l^2 + z(2)^2)*L^2 + l^2*z(4)^2)/(l^2*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))); 
            -cos(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*cos(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))*z(3) - 0.8000000000*cos(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*sin(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2))) + 0.4100000000*sin(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l))) + L*(z(2) + z(4))/(2*sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*sqrt(((L^2 + l^2)*z(3)^2 + (-2*L^2*z(2) - 2*l^2*z(4))*z(3) + (l^2 + z(2)^2)*L^2 + l^2*z(4)^2)/(l^2*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))); 
            -cos(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*cos(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))*z(4) + 0.8000000000*cos(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*sin(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2))) + 0.4100000000*sin(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l))) + L*(z(2) + z(4))/(2*sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*sqrt(((L^2 + l^2)*z(3)^2 + (-2*L^2*z(2) - 2*l^2*z(4))*z(3) + (l^2 + z(2)^2)*L^2 + l^2*z(4)^2)/(l^2*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))); 
            sin(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*cos(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))*z(1) - 0.8000000000*sin(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*sin(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2))) - 0.4100000000*cos(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l))) + ((-z(3)^2 + (-2*z(1) + z(2) + z(4))*z(3) + l^2 + 2*z(1)*z(2) - z(2)*z(4))*L^2 + l^2*(z(3) - z(4))^2)/(2*sqrt(((L^2 + l^2)*z(3)^2 + (-2*L^2*z(2) - 2*l^2*z(4))*z(3) + (l^2 + z(2)^2)*L^2 + l^2*z(4)^2)/(l^2*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l); 
            -cos(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*cos(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)))*z(1) + 0.8000000000*cos(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l)))*sin(atan(-(z(3) - z(4))/sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2))) - 0.4100000000*sin(-atan(L*(z(2) - z(3))/(sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*l))) + L*(z(2) + z(4))/(2*sqrt(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2)*sqrt(((L^2 + l^2)*z(3)^2 + (-2*L^2*z(2) - 2*l^2*z(4))*z(3) + (l^2 + z(2)^2)*L^2 + l^2*z(4)^2)/(l^2*(L^2 + z(3)^2 - 2*z(3)*z(4) + z(4)^2))));
            ];
    end
Z = fmincon(fun, [0.05, 0.05, 0.05, 0.05], [], [], [], [], lb, ub , @mycon, options);
z1 = Z(1);
z2 = Z(2);
z3 = Z(3);
z4 = Z(4);
end

[Malay Agarwal]

Hi @Alessandro Cavalaglio,

Could you share some sample inputs to the function that result in the error? I'd like to reproduce the issue on my end to figure out what's causing the issue. You can attach the sample inputs as a MAT-file.

[Umang Pandey]

Hi Alessandro,

Since the sample input on which the function is failing is not provided, it is not possible to provide the exact solution to the problem you are facing. But based on the error message, suggests a mismatch between the number of constraints and the outputs expected by the fmincon solver.

Here are a few things you can check and modify to resolve this issue:

1. Ensure the Correct Number of Outputs in mycon: The mycon function should return two outputs: inequality constraints (c) and equality constraints (ceq). Ensure that both outputs are correctly defined and returned.
2. Modify the mycon Function: Make sure that mycon always returns two outputs, even if one of them is empty. For instance, if there are no equality constraints, ceq should be an empty array.