Table of Contents
When we write down mathematical expressions we commonly face the dilemma of italicizing the character or not. This article will guide us when to use upright characters and when to not.
Mathematical Text
Common Issues While Writing Mathematical Expressions
If we are writing an equation, an expression, we probably use italic letters on a computerized environment. This style commonly means that if there is no symbol between the letters multiplication symbol is assumed to be there.
For example, consider below expression. It’s very likely that everyone would consider right-hand-side of the equation is as the right-hand side. This is very natural way to type in mathematical context, right?
Now consider we are trying to write a trigonometric function as shown in below. Unfortunately, what we have written on the left hand side could be interpreted as the multiplication of all the letters.
Few more wrong examples are below.
Neatly Written Mathematical Expressions
As demonstrated earlier, if we are writing objects with specific meanings, in
italic type they will not carry the correct meanings. Also, for those single
letter constants i, j as in complex units, we will avoid confusion with
their counterparts, running indices. Therefore, we better write them in upright
mode, and we should be consistent about the way we write them.
NOTE: We should keep running indices, such as i, j, k, in italic form as they are individual variables. If these indices are constant, it’s better to keep them upright.
NOTE: It’s common to write tensors in boldface.
NOTE: Prefer using siunitx package when writing units.
Upright Greek Letters and Upright Special Letters
XeLaTex and LuaLatex
Note that Greek letters and special letters like partial operator is not as straightforward as shown above. In order to get them right, we should follow this answer on Stack Exchange1.
\usepackage{unicode-math}
\symup{\pi} r^2 = Area of circle
\symup{\partial}x = Partial operator on x
\symup{\delta}_{ij} = Kronecker's delta
Pdftex
The upright Greek and special letters for pdftex gets hacky. There could me
many solutions given the flexibility of Latex. You may find two solutions: