By the way, what is the difference between

and

I've seen both used in analysis texts and lecture notes, and is the writer's preference. They typically denote an arbitrary positive real number.

and

Theta is commonly used for angles and theta functions. \vartheta is commonly used to denote the first Chebyshev function (that's the summatory log function over the primes).

and

Pi is used for numerous things, commonly the ratio between a circle's circumference and diameter, but also things like the prime-counting function. The latter is sometimes seen in fluid mechanics texts, and I've also seen it in an analytic number theory paper.

and

I've seen the former used in a lot of physics texts, for density or some other physical quantity. It's sometimes used to define a metric or a representation in representation theory. I've personally never seen the latter outside of a physics text, but I'm sure some author has used it in their paper somewhere.

and

Golden ratio, totient function, amongst many other things. Commonly used to define maps in algebra too.

Also, is Golden Ratio

or ?

I've always used the latter to denote the golden ratio (and the Wiki page seems to define it using that symbol, too). I prefer to adopt the former for the totient function -- although I often use \varphi for homomorphisms.

]]>