How to switch to upright greek in math mode?

Question

I use libertine and newtxmath font packages, they provide upright greek letters. However, there is no way to conveniently swith between italic and upright greek letters. I need a command, simillar to what is discussed here, to change normal greek letters to upright bold symbols.

None of the commands \mathrm, \mathbf, \boldsymbol or \bm makes\theta to appear as \uptheta. Moreover, isomath package does not work with the encoding and its typeface is not desired. I don't want to globally switch to upright greek letters or change the font shape.

\documentclass{report}
\usepackage[T1]{fontenc}
\usepackage[type1]{libertine}
\usepackage[libertine]{newtxmath}
\usepackage{bm} 

\begin{document}
What I get: $\theta \bm{\theta} \mathrm{\theta} \bm{\mathrm{\theta}}$

What I want: $\theta \bm{\theta} \uptheta \bm{\uptheta}$ 
\end{document}

--- Partial Solution ---

I found that a new upgreek command may be defined to replace all greek letter macros (e.g. \theta) with their upside variants (e.g. \uptheta) in its argument. Following example does it for three greek letters. The scope of the command is local, so both variants can be used in a single equation.

\documentclass{report}
\usepackage[T1]{fontenc}
\usepackage[type1]{libertine}
\usepackage[libertine]{newtxmath}
\usepackage{bm} 

\newcommand{\upgreek}[1]{{
\renewcommand{\beta}{\upbeta}
\renewcommand{\theta}{\uptheta}
\renewcommand{\zeta}{\upzeta}
#1
}}

\begin{document}
$\upgreek{\theta} \bm{\upgreek{\theta}} \theta \bm{\theta}$ 
\end{document}

Questions:

• Is it safe to patch \mathrm to run \upgreek on its argument?

Answer 1

You might want to file a feature request to the developer of newtxmath; in the meantime you can change the definitions of the Greek lowercase letters.

\documentclass{report}
\usepackage[T1]{fontenc}
\usepackage[type1]{libertine}
\usepackage[libertine]{newtxmath}
\usepackage{bm} 

\makeatletter
\re@DeclareMathSymbol{\alpha}{\mathord}{lettersA}{11}
\re@DeclareMathSymbol{\beta}{\mathord}{lettersA}{12}
\re@DeclareMathSymbol{\gamma}{\mathord}{lettersA}{13}
\re@DeclareMathSymbol{\delta}{\mathord}{lettersA}{14}
\re@DeclareMathSymbol{\epsilon}{\mathord}{lettersA}{15}
\re@DeclareMathSymbol{\zeta}{\mathord}{lettersA}{16}
\re@DeclareMathSymbol{\eta}{\mathord}{lettersA}{17}
\re@DeclareMathSymbol{\theta}{\mathord}{lettersA}{18}
\re@DeclareMathSymbol{\iota}{\mathord}{lettersA}{19}
\re@DeclareMathSymbol{\kappa}{\mathord}{lettersA}{20}
\re@DeclareMathSymbol{\lambda}{\mathord}{lettersA}{21}
\re@DeclareMathSymbol{\mu}{\mathord}{lettersA}{22}
\re@DeclareMathSymbol{\nu}{\mathord}{lettersA}{23}
\iftx@altnu
  \re@DeclareMathSymbol{\nu}{\mathord}{lettersA}{40}
\fi
\re@DeclareMathSymbol{\xi}{\mathord}{lettersA}{24}
\re@DeclareMathSymbol{\pi}{\mathord}{lettersA}{25}
\re@DeclareMathSymbol{\rho}{\mathord}{lettersA}{26}
\re@DeclareMathSymbol{\sigma}{\mathord}{lettersA}{27}
\re@DeclareMathSymbol{\tau}{\mathord}{lettersA}{28}
\re@DeclareMathSymbol{\upsilon}{\mathord}{lettersA}{29}
\re@DeclareMathSymbol{\phi}{\mathord}{lettersA}{30}
\re@DeclareMathSymbol{\chi}{\mathord}{lettersA}{31}
\re@DeclareMathSymbol{\psi}{\mathord}{lettersA}{32}
\re@DeclareMathSymbol{\omega}{\mathord}{lettersA}{33}
\re@DeclareMathSymbol{\varepsilon}{\mathord}{lettersA}{34}
\re@DeclareMathSymbol{\vartheta}{\mathord}{lettersA}{35}
\re@DeclareMathSymbol{\varpi}{\mathord}{lettersA}{36}
\re@DeclareMathSymbol{\varrho}{\mathord}{lettersA}{37}
\re@DeclareMathSymbol{\varsigma}{\mathord}{lettersA}{38}
\re@DeclareMathSymbol{\varphi}{\mathord}{lettersA}{39}
\makeatother

\begin{document}
What I get: $\theta \bm{\theta}$

What I want: $\uptheta \bm{\uptheta}$ 
\end{document}

Note that \mathbf{\theta} won't do any good, only Latin letters are affected by \mathbf.

---

You can also define \mathup and \mathbfup:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[type1]{libertine}
\usepackage[libertine]{newtxmath}
\usepackage{bm}
\DeclareRobustCommand{\mathup}[1]{\begingroup\changegreek\mathrm{#1}\endgroup}
\DeclareRobustCommand{\mathbfup}[1]{\begingroup\changegreekbf\mathbf{#1}\endgroup}

\makeatletter
\def\changegreek{\@for\next:={%
  alpha,beta,gamma,delta,epsilon,zeta,eta,theta,kappa,lambda,mu,nu,xi,pi,rho,sigma,%
  tau,upsilon,phi,chi,psi,omega,varepsilon,vartheta,varpi,varrho,varsigma,varphi}%
  \do{\expandafter\let\csname\next\expandafter\endcsname\csname\next up\endcsname}}
\def\changegreekbf{\@for\next:={%
  alpha,beta,gamma,delta,epsilon,zeta,eta,theta,kappa,lambda,mu,nu,xi,pi,rho,sigma,%
  tau,upsilon,phi,chi,psi,omega,varepsilon,vartheta,varpi,varrho,varsigma,varphi}%
  \do{\expandafter\def\csname\next\expandafter\endcsname\expandafter{%
    \expandafter\bm\expandafter{\csname\next up\endcsname}}}}
\makeatother

\begin{document}
$\mathup{d}\mathup{\theta}d\theta$

$\mathbfup{d}\mathbfup{\theta}\bm{d}\bm{\theta}$
\end{document}

Answer 2

with xelatex or lualatex you can choose the french style for upright greek letters and have also commands for the bold one:

\documentclass{report}
\usepackage[math-style=french]{unicode-math}
\usepackage{libertine}
\setmathfont{XITS Math}

\begin{document}
What I get: $\theta \mbftheta \alpha \mbfalpha\mbftheta$ \\

What I want: $\theta \alpha\beta \mbfmu$ 
\end{document}