https://s0.wp.com/latex.php?latex=C_%7B%5Ctext%7B%5Ctiny%7BC%7D%7D%7D%28i%29+%3D+%5Cleft%5B+%5Csum_%7Bj%3D1%7D%5E%7BN%7D+d%28i%2Cj%29+%5Cright%5D%5E%7B-1%7D+&bg=ffffff&fg=414141&s=0