In mathematics, the golden ratio, equal to (1 + sqr(5))/2, or about 1.618, is represented by the greek letter phi. I need to include this in a (non-technical) bit of text. My question: which form of the letter is the correct one to use? I know it should be the lower-case phi, but there are two forms of this: I don’t know if they will appear correctly in your browser, but they are shown at the beginning of the Wikipedia article:
The form used in Greek writing has an open left-hand side to the bowl, and the vertical stroke doesn’t project above the bowl; the “math symbol” variant looks like an o with a vertical line through it. The terminology there suggests I should use the “math symbol” form, but the Wiki page for the golden ratio uses an even more extreme “open” form of the letter.
Mathematicians and typographers, your thoughts please?
(Incidentally, every single time I try to type “ratio”, my fingers turn it into “ration”. Does this happen to anyone else?)
I’ve seen both forms of the Greek character in mathematical contexts, but can only remember ever seeing the second case (ϕ) when referring to the Golden Ratio.
I won’t say it’s a firm rule, but I’m confident saying it’s the most common case.
I’ve known the number theoretic and alleged esthetic properties of the golden ratio for decades, but it is only recently that I’ve heard it called \phi. It is not standard in mathematics, not like \pi. That said, I don’t think there is the slightest reason to use one form or the other.
Every single time, and I’m a mathematician. But not one who uses “ratio” much in his own work.
Regarding the golden ratio (typed carefully, there), I’ve certainly seen it denoted by a lower case phi, but I can’t say I’ve noticed which variant. I will say that, when used in math articles for whatever purpose, I almost always see the variant form φ (\varphi in TeX) used, at least in my field.
This question is a bit like asking should I use a or a – though not in italic, of course. They both represent phi. I’ve seen both used. In my experience ϕ is pretty universally used for the normal or Gaussian density, and I think I’ve seen φ a bit more often for the Golden Ratio, but other than that I don’t recall much of a preference.
It seems ϕ is becoming more common now, but I attribute that to the fact that it is the default version in Word and LaTeX.
