How do you create .+?

Question

I would like to display a = b .+ 1

But it is displayed as a = b. + 1 (moves . next to b).

Answer 1

\newcommand{\periodplus}{\mathbin{{.}{+}}}

\( a=b\periodplus 1 \)

TeX (and so LaTeX) doesn't interpret spaces in the code for math formulas, but relies on its predefined rules. For TeX a, . and b represent "ordinary" symbols and + a binary operation symbol.

Consecutive ordinary symbols are set without any space between them; instead, the combination

ordinary binary-operation ordinary

will be set with spaces around the binary operation symbol.

Any subformula can be changed into a binary operation symbol using \mathbin{<subformula>}. I've put both characters between braces to be sure they are interpreted as ordinary symbols in the subformula (they would anyway).

Of course it's possible to say

\( a = b \mathbin{.+} 1 \)

each time, but it's best to have a command for this if it appears more than a couple of times.

Answer 2

If this is MATLAB code, and not regular math, then the lstinline command from the listings package would be useful:

\documentclass{article}
\usepackage{listings,xcolor}
\lstset{language=MATLAB,basicstyle=\ttfamily,stringstyle=\color{red}}
%\lstset{showstringspaces=false} % uncomment this if you don't want spaces in
                                 % strings to get their own symbols
\newcommand{\periodplus}{\mathbin{{.}{+}}}

\begin{document}
The line of MATLAB code \lstinline|a = b .+ 1| should not look like the math
equation \( a=b\periodplus 1 \). And there's more difference between
\lstinline|s = sprintf('x = %d\n',x)| and
\(s = sprintf('x = \%d\backslash{}n',x) \).
\end{document}

I only mention this because I'd never seen .+ as a math operator, but it's used all the time in MATLAB.