Why letters appear bold in equation?

I want to write out the following equations,

$$\bf{V} = F(\boldsymbol{\sigma}) + \bf{e}$$

$$\Delta \bf{V} \approx J \cdot \Delta \boldsymbol{\sigma}$$


For some reason the F and the second Delta are appearing bold, although I do not want them to be bold. How can I resolve this issue?

• Welcome to TeX.SE. Advice: the command \bf is depreciated. For modern LaTeX documents you must use \mathbf{...}. Apr 15 '18 at 21:01
• Not only \bf is deprecated: its syntax would be {\bf V}, but \mathbf{V} is the correct form. Apr 15 '18 at 21:06
• @Sebastiano Your comment should be an answer. Apr 15 '18 at 21:07
• @egreg Thanks a lot for your suggestion. I have add an answer. Apr 15 '18 at 21:09
• @egreg YOU ARE ALWAYS AUTHORIZZATED TO EDIT MY QUESTIONS AND ANSWERS. Apr 15 '18 at 21:15

The command \bf is deprecated. Besides it should be {\bf V}, but the correct form is \mathbf{V}.

Also \bm is better than \boldsymbol (requires the bm package).

\documentclass{article}

\usepackage{amsmath}
\usepackage{bm}

\begin{document}

$$\mathbf{V} = F(\bm{\sigma}) + \mathbf{e}$$

$$\Delta \mathbf{V} \approx J \cdot \Delta \bm{\sigma}$$

\end{document}


• Dear Prof. unfortunately in my profile there is not the motto of the "Barbiere di Siviglia" :-). I'm lent when I think and write. Thank you so much for your cooperation. I do not know what is the unicode symbol of the bow but you keep in mind that there is. Apr 15 '18 at 21:14