http://8.136.99.126/blog/3/667ed5d1bfb9bd49c48885eb

建议用 \left \lfloor xxx \right \rfloor 而不是 \lfloor xxx \rfloor

Example:

$\lfloor{\dfrac12}\rfloor$ $\lfloor{\dfrac12}\rfloor$

$\left\lfloor{\dfrac12}\right\rfloor$ $\left\lfloor{\dfrac12}\right\rfloor$