Bold , italic (and sans-serif) math symbols

Question

I would like to implement the suggestions in the TUGboat 30:3, 2009 about the upright/italic and bold/normal in scalars, vectors and tensors. All this is about math.

I use this font:

\usepackage[charter]{mathdesign}

For vectors, I always used \vec, so I just redefined it like so:

\renewcommand{\vec}[1]{\boldsymbol{#1}}

Now they are bold and italic, just like I want them. Is that even the correct way to do this?

How can I get characters in bold, italic and sans-serif?

I almost got it with this, they are just upright and not italic:

\newcommand{\tens}[1]{\boldsymbol{\mathsf{#1}}}

Answer 1

The cleanest way is to define a new math alphabet:

\DeclareMathAlphabet{\mathbfsf}{\encodingdefault}{\sfdefault}{bx}{n}

and then

\newcommand{\tens}[1]{\mathbfsf{#1}}

If you want italic bold sans serif, just change the first declaration into

\DeclareMathAlphabet{\mathbfsf}{\encodingdefault}{\sfdefault}{bx}{sl}

but keep in mind that the OT1 encoded Computer Modern Sans fonts don't have slanted bold face, so also

\usepackage[T1]{fontenc}

or

\usepackage{lmodern}

is required.

---

You should also consider using \bm of the bm package instead of \boldsymbol, so that \bm{\mathsf{T}} would be equivalent to the \mathbfsf{T} with the first declaration. However there is no predefined sans serif italic math alphabet. So, if you need also sans serif italic, a more economic setting would be

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{bm}

\DeclareMathAlphabet{\mathsfit}{\encodingdefault}{\sfdefault}{m}{sl}
\SetMathAlphabet{\mathsfit}{bold}{\encodingdefault}{\sfdefault}{bx}{sl}

\newcommand{\tens}[1]{\bm{\mathsfit{#1}}}

\begin{document}
$\tens{T}$
\end{document}