# Small integral symbol

I can't understand why an integral of a fraction doesn't resize the integral symbol by itself.

$\text{SAR}=\int_{campione}\dfrac{\bf{\sigma}(r)|\bf{E}(r)|^2}{\bf{\rho}(r)}dr$ I saw this Big integral sign but with bigints nothing changes (and yes, I loaded the package and I erased all those files that work like a cache). I wouldn't write an instruction to make this resize

• INHO, using \dfrac in an inline math expression is almost surely an error. If you need to use \dfrac, switch to displaymath style; a side benefit will be that the integral symbol becomes large automatically. – Mico Jun 4 '16 at 17:57
• Comment aside\bf{\sigma} won't produce a bold σ. For this you should use \boldsymbol{\sigma} or \bm{\sigma} if you load the bm package. – Bernard Jun 4 '16 at 18:14
• I wrote \bf instead \bm – Shika93 Jun 4 '16 at 18:20

$\text{SAR}=\displaystyle\int_{\mathit{campione}}\dfrac{\bf{\sigma}(r)|\bf{E}(r)|^2}{\bf{\rho}(r)}\,dr$,

$\text{SAR}=\int_{\mathit{campione}}\dfrac{\bf{\sigma}(r)|\bf{E}(r)|^2}{\bf{\rho}(r)}\,dr$

Using \bf in LaTeX is not recommended. You have, e.g., \mathbf{}.