Fix COPT interface silently dropping nonzero quadratic objective when Q has an all-zero column

[terryweng03]

Hi, there is a suspected issue in COPT interface.

Problem

The COPT interface (solvers/yalmip2copt.m) uses if any to decide whether to attach the quadratic objective matrix:

if any(interfacedata.Q)        % line 133
    model.Q = interfacedata.Q;
end
...
if any(interfacedata.Q)        % line 195 (cone/expcone extension block)
    model.Q(length(model.obj),length(model.obj)) = 0;
end

interfacedata.Q is a sparse square matrix. any(Q) on a matrix returns a per-column logical row vector, not a scalar. MATLAB's if collapses a non-scalar with an implicit all(...(:)), so the guard actually tests "every column has a nonzero entry" rather than "Q has any nonzero entry".

Minimal reproducer

x = sdpvar(1,1); y = sdpvar(1,1);
F = [0 <= x <= 10, 0 <= y <= 1];
obj = (x-3)^2 + y;            % Q = diag([1,0]): y column all-zero

opt = sdpsettings('solver', 'copt', 'verbose', 1 ,'savesolverinput', 1);
opt.copt.Logging = 1;
opt.copt.LogToConsole = 1;

d = optimize(F,obj,opt);

Variable order [x; y] gives Q = diag([1, 0]) — the y column is all-zero.

• Correct solution: x = 3, y = 0, objective 0.
• Before the fix: COPT receives no Q, minimizes -6x + y + 9, returns x = 10, y = 0 with solver objective -51.