How to express x(1)^2+x(2)^2=y^2 as a constraint in cvx? Thanks very much.

My code is as follows.

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U=[ 2.0647, 0 , -1.8435; 0 , 0.9080 , 0;-1.8435, 0, 1.6475]

w=mvnrnd([0;0;0],inv(Q),1)’;

b=-2*Q*w;

p=B0’*b;

cvx_begin quiet

variables x(2) y;

minimize(quad_form([x’,y]’,U)+[x’,y]*p);
subject to
norm(x)==norm(y);
B1*[x’,y]’<=[0;0];

cvx_end

cvx_x=B0*[x’,y]’;