# Bold for vectors, tensors, and matrices in mathematical formula (Springer journal)

I am preparing to send a paper to springer journal, In (instructions for Authors-> Scientific style) there is an instruction said: Bold for vectors, tensors, and matrices. I used \bm to bold to do that:

\begin{equation}
\frac{d\bm{P}_k^-}{dt}=\bm{F}_x(\bm{m}_k^-(t),t,\bm{\theta})\bm{P}_k^- +\bm{P}_k^- \bm{F}_x^T(\bm{m}_k^-(t),t,\bm{\theta}) + \Sigma(\bm{m}_k^-(t),t,\bm{\theta})
\label{eq:Euler}
\end{equation}


I get : but in springer journal the equation looks like: How can I fix that?

• Also the derivative d's need to be upright, which is the only logical way to do it. But sadly Springer uses italic T's for transposed, which is inconsistent.
– lblb
May 12, 2017 at 21:28
• @lblb most mathematicians I know don't use straight d's, they look bad May 12, 2017 at 22:06

You have to use mathbf to produce the upright math fonts.

Since they usually represent vectors, you can renew the \vec command.

Also I created a derivative operator \drv which prints an upright d (as a derivative sign) keeping the spacing (at least to its right) that is present in the text

Here an implementation

   \documentclass{article}
\usepackage{amsmath}
\renewcommand{\vec}{\mathbf{#1}}
\DeclareRobustCommand*{\drv}{\mathop{}\!\mathrm{d}}
\begin{document}
\begin{equation}
\frac{\drv\vec{P}_k^-}{\drv t}=\vec{F}_x(\vec{m}_k^-(t),t,\vec{\theta})\vec{P}_k^- +\vec{P}_k^- \vec{F}_x^T(\vec{m}_k^-(t),t,\vec{\theta}) + \Sigma(\vec{m}_k^-(t),t,\vec{\theta})
\label{eq:Euler}
\end{equation}

\end{document} Thanks to @GustavoMezzetti and @lblb for their insightful remarks

EDIT

Since the user asked, I provide a solution, which I don't know if optimal, concerning the bold math symbols.

The "normal" way in fact should be

1. Load bm and upgreek

2. Substitute the greek letter with its upshape, ie theta becomes uptheta

3. Call \bm{\uptheta} instead of vec

If one wants to keep the vec version, instead, has only to substitute theta with uptheta to obtain what he wants:

\documentclass{article}
\usepackage{amsmath,bm,mathtools,upgreek}
\renewcommand{\vec}{\bm{\mathrm{#1}}}
\DeclareRobustCommand*{\drv}{\mathop{}\!\mathrm{d}}
\begin{document}
\begin{equation}
\frac{\drv\vec{P}_k^-}{\drv t}=\vec{F}_x(\vec{m}_k^-(t),t,\vec{\uptheta})\vec{P}_k^- +\vec{P}_k^- \vec{F}_x^T(\vec{m}_k^-(t),t,\vec{\uptheta}) + \Sigma(\vec{m}_k^-(t),t,\vec{\uptheta})
\label{eq:Euler}
\end{equation}

\end{document} • +1, but I beg to disagree with the \ensuremath: IMHO, a command like \vec should be used only in math mode, and rise an error if not.
– GuM
May 12, 2017 at 21:12
• @GustavoMezzetti Ok, I understand and I had doubts myself. I removed the \ensuremath May 12, 2017 at 21:12
• You'd have to use upright derivative d's too.
– lblb
May 12, 2017 at 21:27
• @lblb right. done May 12, 2017 at 21:36
• But, wait: I think that with \drv(x^2) (say) we are going to have a surpise…!
– GuM
May 12, 2017 at 21:47