在利用CVX工具箱求解二階錐規劃時，加了一條不等式約束，結果報錯，在google搜到的結果是該約束非凸.
（1）首先對該約束的凸性存在疑惑
（2）如何修改可以把該約束由非凸轉凸？
code如下：

1. %%%% Use CVX solve the SOPC problem
2. % cvx version
3. opt_n = 2*N_global + 1;
4. e_b = 1e1;
5. e_d = 1e-4;
6. e_g = 800;
7. cvx_begin
8.     variable b(opt_n) complex
9.     minimize( norm(Tb*b-ab))
10.     subject to
11.     norm(Td*b) <= sqrt(e_d);
12.     norm(Tb*b) >= sqrt(e_b);
13.     norm(b) <= sqrt(e_g);
14.     
15. cvx_end

報錯結果如下：

1. Warning: A non-empty cvx problem already exists in this scope.
2.    It is being overwritten. 
3. > In cvxprob (line 28)
4.   In cvx_begin (line 41)
5.   In demostration_scatter_without_to_2D_8_27_dft_add_acc (line 59) 
6. Error using cvxprob/newcnstr (line 192)
7. Disciplined convex programming error:
8.    Invalid constraint: {convex} >= {real constant}
9.  
10. Error in  >=  (line 21)
11. b = newcnstr( evalin( 'caller', 'cvx_problem', '[]' ), x, y, '>=' );
12.  
13. Error in demostration_scatter_without_to_2D_8_27_dft_add_acc (line 64)
14.     norm(Tb*b) >= sqrt(e_b);