How to get currently used math font? Or: How to ensure use of math font in pgfplots axis labels and ticks even if overwritten by text string?

Question

Preface:

An axis plotted with pgfplots is usually using the current math font for its ticklabels. But if they are overwritten by e.g. xticklabels={-8,-6,...,8} then the current text font is used. Also an axis label ylabel={Y} would be in text font unless put explicitly in math mode ylabel={$Y$}. However it would be nice, if one hadn't to do so.

Question:

I'm aiming to ensure that pgfplots always uses the current math font. But please assume that the classic font commands like \rmfamily are screwed up by the corporate design I'm supposed to use, e.g. assume: \renewcommand{\rmdefault}{\sfdefault}

It works if I explicitly define a font

\newcommand{\pgfmathfont}{\fontfamily{pxfonts}\selectfont}

and pass it to pgfplots together with assume math mode=true:

\begin{axis}[
font = \pgfmathfont, 
tick label style={/pgf/number format/assume math mode=true}
]

But it requires that I insert the name of the current math font. How can I do that automatically? How to get the currently used math font to insert it into the macro?

---

MWE

\documentclass{beamer}

\usetheme{Warsaw}
\usefonttheme{professionalfonts}
\usepackage{pxfonts}
\usepackage{pgfplots}

% screwed up by Corporate Design
\renewcommand{\rmdefault}{\sfdefault}

% I'd like this line to be generic!
\newcommand{\pgfmathfont}{\fontfamily{pxfonts}\selectfont}
%           put current math font here   X

\begin{document}

\begin{frame}

This is a basic equation:   
\[ x + y = 42\]

\begin{tikzpicture}
    \begin{axis}[
%   font = \rmfamily, % makes no sense here
    font = \pgfmathfont, 
    xlabel={$x$-label: I want to be in math font!},
    ylabel={Y},
    xtick={-4,-3,...,4},
    xticklabels={-8,-6,...,8},
%   xticklabels={$-8$,$-6$,...,$8$}, % does not work
    tick label style={/pgf/number format/assume math mode=true}
    ]

    \addplot {x^2};

    \end{axis}
\end{tikzpicture}

\end{frame}

\end{document}

---

Everything related to fontspec is no option at all!

Thank you!

Answer 1

Define a new style:

\documentclass{beamer}

\usetheme{Warsaw}
\usefonttheme{professionalfonts}
\usepackage{newpxtext,newpxmath}
\usepackage{pgfplots}

% screwed up by Corporate Design
\renewcommand{\rmdefault}{\sfdefault}

\pgfplotsset{
  typeset ticklabels as math/.style={
    /pgfplots/typeset ticklabel/.code={$##1$},
  },
}


\begin{document}

\begin{frame}

This is a basic equation:   
\[ x + y = -8\]

\begin{tikzpicture}
    \begin{axis}[
    xlabel={$x$-label: I want to be in math font!},
    ylabel={Y},
    xtick={-4,-3,...,4},
    xticklabels={-8,-6,...,8},
    typeset ticklabels as math,
    tick label style={/pgf/number format/assume math mode=true}
    ]

    \addplot {x^2};

    \end{axis}
\end{tikzpicture}

\end{frame}

\end{document}

Note that the combination newpxtext with newpxmath should be preferred to pxfonts, because it cures some drawbacks from the unmaintained older package.

Answer 2

The ticklabels could be calculated from the ticks using

xticklabel={\pgfmathparse{2*\tick}\pgfmathprintnumber{\pgfmathresult}}

But if you really want to use tick label style={/pgf/number format/assume math mode=true} you have to surround \pgfmathprintnumber{} by $...$. Note that assume math mode=true should only be used if you are sure that math mode is active. From the pgfmanual: " ... the final number is typeset as-is, no further checking is performed."

xticklabel={\pgfmathparse{2*\tick}$\pgfmathprintnumber{\pgfmathresult}$},
tick label style={/pgf/number format/assume math mode=true}

\documentclass{beamer}
\usetheme{Warsaw}
\usefonttheme{professionalfonts}
\usepackage{newpxtext,newpxmath}% as suggested by @egreg
\usepackage{pgfplots}

% screwed up by Corporate Design
\renewcommand{\rmdefault}{\sfdefault}

\begin{document}
\begin{frame}
This is a basic equation:   
\[ x + y = 42\]
\begin{tikzpicture}
    \begin{axis}[
    font = \rmfamily,
    xlabel={$x$-label: I want to be in math font!},
    ylabel={Y},
    xtick={-4,-3,...,4},
    xticklabel={\pgfmathparse{2*\tick}\pgfmathprintnumber{\pgfmathresult}},
    ]
    \addplot {x^2};
    \end{axis}
\end{tikzpicture}
\end{frame}
\end{document}

Another possibility is

xticklabels={$-8$,$-6$,$...$,$8$}

as suggested by @percusse in a comment to your question. Note that $...$ is used.

---

If the tick labels can not be calculated from the tick values you can define an array

\def\myxticklabels{{1.9, 7, 42, 5, 5, 6, 8, 5, 0.720}}

and use

xticklabel={\pgfmathparse{\myxticklabels[\ticknum]}\pgfmathprintnumber{\pgfmathresult}},

Code:

\documentclass{beamer}
\usetheme{Warsaw}
\usefonttheme{professionalfonts}
\usepackage{newpxtext,newpxmath}% as suggested by @egreg
\usepackage{pgfplots}

% screwed up by Corporate Design
\renewcommand{\rmdefault}{\sfdefault}

\begin{document}
\begin{frame}
This is a basic equation:
\[ x + y = 42\]
\begin{tikzpicture}
    \def\myxticklabels{{1.9, 7, 42, 5, 5, 6, 8, 5, 0.720}}
    \begin{axis}[
    font = \rmfamily,
    xlabel={$x$-label: I want to be in math font!},
    ylabel={Y},
    xtick={-4,-3,...,4},
    xticklabel={\pgfmathparse{\myxticklabels[\ticknum]}\pgfmathprintnumber{\pgfmathresult}},
    /pgf/number format/use comma
    ]
    \addplot {x^2};
    \end{axis}
\end{tikzpicture}
\end{frame}
\end{document}