How to create constraints inside a loop?

[Daniel Dimitrov]

Hello,

I an trying to create a YALMIP constraint object with a loop.

I the end I need something of the type

constraint = [x1 + x2 + x3 +....+xN >= 0]

So, instead of typing all that I'm trying to create it using a loop, but I have the feeling that YALMIP doesn't work as I expect it. Is this correct

x = sdpvar(N,1,'full');
constraints = 0;

for  i = 1:N
constraints = x(i) + constraints
end

constraints = [constraints >=0]

[Johan Löfberg]

In your for-loop your adding variables and constraints, which doesn't make sense.

A for-loop would be

thesum = 0;

for  i = 1:N


thesum = x(i) + thesum
end
constraints = thesum >= 0


of course, in reality, you would preferably use some vectorization

constraints = sum(x)>=0

[Daniel Dimitrov]

I have tried that but I can still see that but I still see that after a couple of iterations of the loop - the variable thesum
still stays of size "sdpvar 1x1". Shouldn't it grow with i? Is there a way that I can eventually what the constraint looks like? I'm afraid that the after the loop is finished, the constraints won't look as I would expect them to

[Johan Löfberg]

No, why should it. Do you expect thesum to grow in this matlab code

x = [1 2 3];
thesum = 0;
for i = 1:3
 thesum = thesum + x(i);
end

Your expression x1 + x2 + x3 +....+xN is a scalar 1x1.

[Daniel Dimitrov]

I see, this makes sense, thank you