10

I'm using newtxmath with the slanted and libertine option in order to get standard slanted greek letters in mathmode as well as the option for upright greek letters.

My question concerns a common two letter variable consisting of a captial Delta and a variable (either latin or greek). It is used in physics to denote the finite increase of a quantity (cf. IUPAP Red Book, Sec. 5.2). The problem when simply typing \upDelta x it can lead to results that look confusing:

Meaning of expression unclear

The Problem is that the spacing between all symbols is equal and it is not clear that the Delta belongs to the following variable.

My attempt now is to remove the space after the Delta that denotes hidden multiplication. In the accepted answer to a similar question (Two letter variable names) the use of \mathit{} was recommended:

\mathit{NA} \neq NA = N \cdot A

enter image description here

This, however, doesn't work if greek letters are involved. The second answer says removing the space with hspace{-0.1em}. This works for a lot of letters but in some cases the Delta clashes with the variable. Furthermore, I don't know if ´0.1em` is the right amount of space to be removed, for me this choice seems rather arbitrary.

This MWE illustrates the problem at hand:

\documentclass{scrartcl}

\usepackage{mathtools}
\usepackage{libertine}
\usepackage[slantedGreek,libertine]{newtxmath}

\newcommand{\updel}[1]{\upDelta\hspace{-0.1em}#1}
\newcommand{\sldel}[1]{\Delta\hspace{-0.1em}#1}

\begin{document}
Doesn't work:
\begin{equation}
  \mathit{\upDelta\Phi} \quad \mathit{\upDelta A}\text{.}
\end{equation}
Works only with \(\Phi\) but not with \(A\):
\begin{equation}
 \updel{\Phi} \quad \updel{A}\text{.}
\end{equation}
With slanted \(\Delta\):
\begin{equation}
 \sldel{\Phi} \quad \sldel{A}\text{.}
\end{equation}

\end{document}

enter image description here

A different approach would be to add spaces before and after \upDelta x but I couldn't say how much space is appropriate.

  • The spacing seems correct and necessary with $\upDelta\Phi\upDelta A$; why using \mathit? – egreg Oct 25 '13 at 19:22
  • 1
    In physical chemistry the uppercase delta is used to denote a change in an extensive quantity for a process (e.g. ΔH). The IUPAC Green Book (section 2.11.1 (iii) uses an upright symbol for those. – clemens Oct 25 '13 at 23:16
  • @egreg: I edited my question. I hope this makes it clear why the spacing can be problematic. – frankundfrei Oct 26 '13 at 12:08
  • @cgnieder: Thank you, I added the IUPAP Red Book as a source. In physics the Delta is used in a similar way. – frankundfrei Oct 26 '13 at 12:10
  • @frankundfrei in chemistry though it clearly is an operator (Δ = ∂/∂ξ) so it probably should get the same spacing as other operators. Interestingly enough the IUPAC Green book doesn't seem to care and uses the same spacing as for variables... – clemens Oct 26 '13 at 12:17
7

You don't want to remove the space between Δ and the following letter, but rather adding a thin space before it:

\newcommand{\updel}{\mathop{}\!\upDelta}

There is no “hidden multiplication” if the symbol is defined similarly to the differential.

\documentclass{scrartcl}

\usepackage{mathtools}
\usepackage{libertine}
\usepackage[slantedGreek,libertine]{newtxmath}

\newcommand{\updel}{\mathop{}\!\upDelta}

\begin{document}
Here's an example
\begin{equation}
 x \updel\Phi + N \updel A.
\end{equation}

\end{document}

enter image description here

  • That looks good! Could you please say a word or two about what \mathop{}\! does? \! is is a negative space but I don't understand what \mathop{} does and how you determined the size of the space (just because it looks OK, or is there a proper rule of how much space there should be?). – frankundfrei Oct 26 '13 at 17:16
  • 2
    @frankundfrei You can read the explanation here – egreg Oct 26 '13 at 17:21

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