While we're on the topic, all the journals I'm familiar with require punctuation like full stops (aka periods) to be included in displaystyle maths expressions. There is a some logical justification for this, but it looks awful, and can be downright confusing depending on the sort of notation employed. It particularly irks me to see a spare comma tagged on to the end of a tensor calculus expression, that's supposed to be understood in the context of the surrounding prose, rather than the adjecant mathematical expression.