I just received a .tex file from a colleague of mine and the file has several \rm commands in math mode. We are both using windows, but he is using WinEdt and I'm using TeXmaker. On his computer this file is compiled without errors, but on my notebook I get error messages saying \rm is an undefined command. What is going on?
Thank you very much.
\rm is not defined in the latex format. Some classes define it for compatibility
with LaTeX 2.09 (that is, documents written before 1993). The Koma classes previously defined it with a warning but more recent releases do not define it, so you get an error if it is used.
After 20 years of deprecation the scrartcl author not unreasonably thought it should no longer be needed.
The editor (winedt, texmaker, etc.) you use to write the file has no bearing on this at all.
The editor you use is irrelevant. What matters is which vintage of scrartcl you use. Until recently (June 2016), the KOMA-script document classes -- scrartcl, scrreprt, and scrbook -- sort of tolerated the deprecated font-switching instructions \rm, \bf, \it, etc., while issuing copious warning messages if they were encountered. In June 2016, however, support for these directives in the KOMA-Script classes ceased entirely.
If you truly, positively, absolutely must use \rm and the other deprecated font-switching instructions, you could add the following code -- which is lifted straight from article.cls -- to your preamble:
\DeclareOldFontCommand{\rm}{\normalfont\rmfamily}{\mathrm}
\DeclareOldFontCommand{\sf}{\normalfont\sffamily}{\mathsf}
\DeclareOldFontCommand{\tt}{\normalfont\ttfamily}{\mathtt}
\DeclareOldFontCommand{\bf}{\normalfont\bfseries}{\mathbf}
\DeclareOldFontCommand{\it}{\normalfont\itshape}{\mathit}
\DeclareOldFontCommand{\sl}{\normalfont\slshape}{\@nomath\sl}
\DeclareOldFontCommand{\sc}{\normalfont\scshape}{\@nomath\sc}
Note that \sl and \sc will only work in text mode, but not in math mode. See this posting for more information on this subject.
A full MWE:
\documentclass{scrartcl}
% The following code is from the file `article.cls`
\DeclareOldFontCommand{\rm}{\normalfont\rmfamily}{\mathrm}
\DeclareOldFontCommand{\sf}{\normalfont\sffamily}{\mathsf}
\DeclareOldFontCommand{\tt}{\normalfont\ttfamily}{\mathtt}
\DeclareOldFontCommand{\bf}{\normalfont\bfseries}{\mathbf}
\DeclareOldFontCommand{\it}{\normalfont\itshape}{\mathit}
\DeclareOldFontCommand{\sl}{\normalfont\slshape}{\@nomath\sl}
\DeclareOldFontCommand{\sc}{\normalfont\scshape}{\@nomath\sc}
\begin{document}
$a$ $\it a$ $\rm a$ $\bf a$ $\sf a$ $\tt a$
\end{document}
scrartclclass will indeed issue copious warnings about deprecated commands such as\rm. I guess one of your front-ends is set to simply ignore these warnings whereas the other is not. :-) See the posting Is there any reason not to use \let to redefine a deprecated control sequence to the currently recommended one? and, in particular, Ulrike Fischer's answer for more information on the subject of deprecated font-switching commands. – Mico Nov 17 '16 at 15:59scrartcl(3.21) the use of\rmcauses an error. I'm guessing they have different versions of KOMA-script, where one only gives a warning and the other (newer) gives an error. – Torbjørn T. Nov 17 '16 at 16:03scrartclis installed on your system and on that of your co-author? – Mico Nov 17 '16 at 16:09\rmand\bf(if, but here I should check LaTeX2e predates the Koma classes). But I just don't understand at all why it is so universally repeated not to use\rm,\bf, ... they are supported by article class and the LaTeX team will definitely not break compatibilty suddenly after 20 years with old documents. They accomplish something which has its value. For example I may really want\bfand not\bfseries. Why force me to write\normalfont\rmfamily\bfseriessuddenly after twenty years ? – Nov 17 '16 at 16:47