Testing MathJax

$$\log\sum_{i=1}^n\exp(f(x_i))$$ $$\log\sum_{i=1}^n\exp(f(x_i))$$ And inline: $\log\sum_{i=1}^n\exp(f(x_i))$ and $\log\sum_{i=1}^n\exp(f(x_i))$