Multiplication operation

Good day, I have a problem with a multiplication operation in CVX.

variables alfa(m) temp;
maximize sum(alfa) - 0.5*temp;
subject to
    temp = 0;
    for i=1:m
        for j=1:m
            temp = temp + alfa(i)*alfa(j)*labels(i)*labels(j)*K_matrix(i,j);
    0 <= alfa <= C;
    sum(alfa.*labels) == 0;

And output:

Disciplined convex programming error:
Invalid quadratic form(s): not a square.
Error in main (line 23)
temp = temp + alfa(i)*alfa(j)*labels(i)*labels(j)*K_matrix(i,j);

So for sure I do the operation in a wrong way, but can you give me advice how to change it to a proper form?

I would eliminate temp altogether—in fact, the temp = 0 term will eventually force an error when you reach cvx_end, for the reasons explained in Assignment and expression holders.

Then I would replace the objective term with this:

minimize (alfa.*labels)'*K_matrix*(alfa.*labels)

I think you should be able to confirm by inspection that this is correct.

I’ve changed my code to this for using your advice

temp = (alfa.*labels)';
maximize sum(alfa) - 0.5*temp*K_matrix*(alfa.*labels);

And it seems to work properly now. So thanks.

Very good, but why use temp here at all? And if you insist on using temp, why not use it for both the left and right-hand sides of the quadratic form? It seems you’re simply making your code less readable for no practical reason.