# Question about terminology: ch = cosh?

Gold Member
I am reading the draft of a paper written by someone whose native language was not English and so who might not have been using the same abbreviations that I am familiar with, or maybe he was using standard ones and I am simply not familiar with the abbreviations involved. I can't ask him, as he is deceased. I quote:
"The properties of the event plane are described by the homogeneous two-dimensional Lorentz group L:
x' = xchθ + τshθ
τ' = xshθ + τchθ
where the hyperbolic angle θ is the transformation parameter. The relation of θ to the relativity velocity β is given by β = thθ. The coordinate τ = ct,..."

What are ch, sh, and th? Did he mean cosh, sinh, and tanh? Are his abbreviations standard?
Thanks.

## Answers and Replies

Mentor
What are ch, sh, and th? Did he mean cosh, sinh, and tanh?

I think so.

Are his abbreviations standard?

Not in English at least, as far as I know.

1 person
Science Advisor
What are ch, sh, and th? Did he mean cosh, sinh, and tanh? Are his abbreviations standard?
Yes. I often write ch in place of cosh. Especially when I'm in a rh.

1 person
Mentor
Yeah, it can be uncomfortable writing stuff when you have a rash.

I admit I don't read much stuff that uses hyperbolic functions.

yuiop
"The properties of the event plane are described by the homogeneous two-dimensional Lorentz group L:
x' = xchθ + τshθ
τ' = xshθ + τchθ
where the hyperbolic angle θ is the transformation parameter. The relation of θ to the relativity velocity β is given by β = thθ. The coordinate τ = ct,..."

What are ch, sh, and th? Did he mean cosh, sinh, and tanh? Are his abbreviations standard?
He is talking about the Lorentz transformation in terms of rapidity rather velocity.
See http://en.wikipedia.org/wiki/Lorentz_transformation#Rapidity and http://en.wikipedia.org/wiki/Rapidity
It is clear from those links that he does mean cosh, sinh, and tanh.

1 person