Katex render error

[nonlinearthink]

Code:

y_{i+1} = \begin{cases}
   y_i+1 &\text{if } e_{i+1} \gt 0.5\\
   \\
   y_i &\text{if } e_{i+1} \le 0.5\\
\end{cases}

Should looks like:

$$ y_{i+1} = \begin{cases} y_i+1 &\text{if } e_{i+1} \gt 0.5\\ \\ y_i &\text{if } e_{i+1} \le 0.5\\ \end{cases} $$

But it got: