Error using .* (line 262) Disciplined convex programming error: Invalid quadratic form(s): not a square

Thanks all.

The picture should be less than or equal to rouk’k
This is my question. Here I want to prove it is quasi-concave. So I expressed the denominator in the form of a norm, finally, I can prove that the function of the up-level set can be expressed as SOC.
But there was an error in cvx: Error using . (line 262) Disciplined convex programming error: Invalid quadratic form(s): not a square.*
Part of my code is

variable cauy(M,K)
variable rou(K,K)
%% -----------------------------calculate subject 2 left
X = zeros(K,K,M);
for k=1:K
    for ii=[1:k-1,k+1:K]
        for m=1:M
            X(ii,k,m) =( 4/pi*abs( ( BETAA(m,k) * sqrt(Gammaa(m,ii)) * cauy(m,ii) / BETAA(m,ii) ) * ( sum( BETAA(:,k) .* (Gammaa(:,ii).^0.5) .* cauy(:,ii) ./ BETAA(:,ii) ) - BETAA(m,k) * sqrt(Gammaa(m,ii)) * cauy(m,ii) / BETAA(m,ii) ) ) )^0.5;
        sb5_left(ii,k) = norm( X(k,ii,**:**) );

In my question, only cauy is a variable, and all of the arguments are greater than or equal to zero. I hope you can help me. Thank you

X(ii,k,m) is kind of a mess. It appears to violate multiple DCP rules. Even if it were DCP-compliant, it isn’t affine, and therefore taking its norm is not allowed. Please re-read Why isn’t CVX accepting my model? READ THIS FIRST! and the CVX Users’ Guide.

help cvx/norm

Disciplined convex programming information:
norm is convex, except when P<1, so an error will result if
these non-convex “norms” are used within CVX expressions.
norm is nonmonotonic, so its input must be affine.

Dear Stone, thank you for your reply. Because of the variable’s product that appears in my expression, I violated CVX’s rules. But can you tell me how to change it in this situation? Thank you.

I am presuming this is non-convex unless someone shows otherwise.

I doubt CVX is going to be able to solve your problem, even if it is convex (and of that I remain skeptical)

thanks for your reply!