Set perfect limits in the sum in latex jupyer

sum_limits_upper_lower.md

Many times you want to write the formulae in which the limits need to be written up side and low side of the sigma. But the problem happens when it is not written as expected.

In such times, just add \displaystyle brfore the sum:

The problem:

$$\varrho(\tau) = \frac{ \sum_{t=1}^{T-\tau} (y_t - \mu) (y_{t + \tau} - \mu)} {(T - \tau)\varrho^2}$$

The solution

$$\varrho(\tau) = \frac{\displaystyle \sum_{t=1}^{T-\tau} (y_t - \mu) (y_{t + \tau} - \mu)} {(T - \tau)\varrho^2}$$