```
cvx_begin
variables Pb Pj
expressions b e u
b = log(1+ Pb * real(Hb * Hb')/sigma)/log(2);
e = log(Pj1 * real(Gj * Gj') + Pb1 * real(Gb * Gb')+sigma)/log(2)...
+ (real(Gj * Gj')*inv_pos(((real(Gb * Gb') * Pb+Pj * real(Gj * Gj')+sigma) * log(2))))*(Pj - Pj1)...
+ (real(Gb * Gb')*(Pb - Pb1))/((real(Gb * Gb') * Pb+Pj * real(Gj * Gj')+sigma) * log(2));
u = log(Pj * real(Gj * Gj') + sigma)/log(2);
minimize b-e+u
```

subject to

I encountered this error while running cvx, how can I fix it?