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# Error happen when doing optimization by using "surrogateopt"

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HUNG JUI CHIU on 22 Apr 2021
Answered: Stephan on 22 Apr 2021
I am trying to do optimization by using "surrogateopt" function.
I got an error "Objective function must return a scalar value".
And I couldn't find the problem.
clear
close all
clc
h = 0.01;
t = 0:h:10;
x = [0 0]';
for i = 1:1001
x1(i) = x(1);
x2(i) = x(2);
if x1(i) >0
a = pi/3;
elseif x1(i)<=0
a = -pi/3;
end
A = [cos(a) sin(a);
sin(a) cos(a)];
B = [0 1]';
intcon = 1;
lb = -1;
ub = 1;
obj =@(u) fun(A, x, B, u);
u = surrogateopt(obj, lb, ub, intcon);
x = fun(A, x, B, u);
end
figure
plot(x1, x2)
grid on
function f1 = fun(A, x, B, u)
f1 = 0.8*A*x+B*u;
end
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### Accepted Answer

Stephan on 22 Apr 2021
f1 is a 2x1 vector - the objective of an optimization has to be a scalar. Thats the error. You need a criterion that expresses the success of your optimization as a scalar.
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