[Tex/LaTex] What free math font could/should accompany Linux Libertine and Linux Biolinum

fontslibertinemath-modexetex

Well, the title of the question pretty much says everything. To be more precise: I'd like to know (1) what font would be visually suitable to use with Linux Libertine and/or Linux Biolinum as the main text font (I haven't decided which of the two I'll use) and (2) how to enable it (as a math font) in XeTeX.

Best Answer

A good guide on what factors to consider when mixing fonts is Thierry Bouche's Diversity in math fonts article in TUGboat, Volume 19 (1998), No. 2.

The most important aspect is to use the same font for text and math letters (as well as letter-like symbols as \partial or \infty). This has drawbacks as some letters will suffer from spacing problems, but compared to the other option (using totally different math letters), it's really a lesser evil. Of course, if this is not acceptable to you, then you should first choose the math font and then use the same font for text, but that limits your font choices dramatically.

Once you've assigned the text font to the math letters, the remaining choices you face is for the geometric symbols, the delimiters and the big operators (\sum, \int, \bigcup etc.). The main consideration is color (how bold the symbols are) and the shape of the symbols (mainly the shape of sum or integral symbols, especially if you use them often). Compared to Libertine, XITS and Asana are a bit too bold (especially true for the sum symbol), Latin Modern is a bit too light (especially +, \otimes, etc.), and Cambria has a very huge \sum symbol, huge \otimes and \oplus as well as very bold \bigcup. Thus, which font will look better will depend on what type of math you're typing, and none will be perfect.

Here's a sample to show the results of this font mixing with Libertine. Notice the spacing problems around the f in f(r_k) and \Sigma_c f(r) due to the fact that's it's a text font we're using for math. I've not set all letter-like symbols to come from Libertine (only \infty), so there's still room for improvement. (Note also the missing parenthesis in one of the formulas with Latin Modern Math.)

libertine with different math fonts

\documentclass{article}

\usepackage{amsmath}

\usepackage{fontspec}
\usepackage{unicode-math}

\setmainfont{Linux Libertine O}

\newcommand{\setlibertinemath}{%
% use Libertine for the letters
\setmathfont[range=\mathit/{latin,Latin,num,Greek,greek}]{Linux Libertine O Italic}
\setmathfont[range=\mathup/{latin,Latin,num,Greek,greek}]{Linux Libertine O}
\setmathfont[range=\mathbfup/{latin,Latin,num,Greek,greek}]{Linux Libertine O Bold}
%\setmathfont[range={"2202}]{Linux Libertine O}% "02202 = \partial % doesn't work
\setmathfont[range={"221E}]{Linux Libertine O}% "0221E = \infty
% etc. (list should be completed depending on needs)
}

\newcommand{\sample}{%
When computing the sums $\sum_{k=0}^{+\infty}{f(r_k)}$ of $f$ the integral representation of $K_0(x)$ may be used.
\[
  \eta(r)\frac{\partial f}{\partial r} + 2\Sigma_cf(r)
    = \sum_{k=0}^{+\infty}{K_0\mathopen{}\left(\frac{\lvert r - r_k \rvert}{L}\right)} 
    = \int_{0}^{\infty}{e^{-\left(z+\frac{r^2}{4L^2\pi}\right)} \frac{dz}{2z}}.
\]
We then use
\[
  \bigcup_{\lambda \in \Lambda}{U_\lambda} \cap  \bigsqcup_{\delta > 0}{G_\delta} = \bigcap_{i \in I}{\mathbf{A}_i}
  \quad \text{so that} \quad 
  u \otimes w \oplus v = 0.
\]
}

\pagestyle{empty}

\begin{document}

\section{Libertine + Latin Modern}
\setmathfont{Latin Modern Math}\setlibertinemath
\sample

\section{Libertine + Cambria}
\setmathfont{Cambria Math}\setlibertinemath
\sample

\section{Libertine + XITS}
\setmathfont{XITS Math}\setlibertinemath
\sample

\section{Libertine + Asana}
\setmathfont{Asana Math}\setlibertinemath
\sample

\end{document}
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