keep getting "too many output arguments" error while using the optimization tool box

i was trying to use the tool box to do an optimazation but it just not working. i keep getting the same error meaasage.

here's my objective function

function f=spring_fun(x)

f=(pi^2*x(2)*x(3)^2*(x(1)+2))/4;

end

and my constraints function:

function g=springcon(x)

G=25.5e6; %shear modulus A
%G=41.4e6; %shear modulus T
%G=79.3e6; %shear modulus S
Fmax=5000;
Cf=(4*(x(2)/x(3))-1)/(4*(x(2)/x(3))-4)+(0.615*x(3))/x(2);
K=(G*x(3)^4)/(8*x(1)*x(2)^3);
singma_p=1500/K;
lf=(Fmax/K)+(1.05*(x(1)+2)*x(3));
smax=1.3e9;
sigma_pm=6;
Dmax=3;
dmin=0.2;
lmax=14;
sigma_w=1.25;
Fp=1500;


g(1)=(8*Cf*Fmax*x(2)/pi*x(3)^3)-smax;
g(2)=lf-lmax;
g(3)=dmin-x(3);
g(4)=x(2)-Dmax;
g(5)=3-(x(2)/x(3));
g(6)=sigma_p-sigma_pm;
g(7)=sigma_p+((Fmax-Fp)/K)+1.05*(x(1)+2)*x(3)-lf;
g(8)=sigma_w-((Fmax-Fp)/K);

it just say "too many output argument" can someone tell me what's going on?please.

thank you.

Answer 1

[Brendan Hamm]

Your non-linear constraint function needs to pass 2 output arguments back with the following calling signature:

function [c,ceq] = nonlcon(x)

as described here https://www.mathworks.com/help/optim/ug/nonlinear-equality-and-inequality-constraints.html

The outputs will enforce the constraints,

If you do not have one of the constraints then you can assign the output the empty array. For example with no non-linear equality you pass the empty array for that output.

function [c,ceq] = nonlcon(x)
    c = x.^4; % Constraint we do have
    ceq = []; % No equality constraint
end