Working in engineering, this comes up way too frequently. Which one is correct?

1) Let Di be *an* mx1 vector...
2) Let Di be *a* mx1 vector...

:-P Thoughts would be appreciated

Ahhh. :)

Well clearly the first sounds more correct if read aloud (or in one's head). And is the one I'd be inclined to go for. I'm pretty sure that some people write things like 'An historic event' and get away with it, even though that only makes sense if you drop the 'h' entirely.

I'll be honest, I'm not entirely sure if there's a rule exception for this one. I'd suggest finding the most pedantic reviewer you know and asking them. They may be wrong, but ultimately they're the ones you would have to get it past!

Yeah, my general advice is based on sound, and it isn't that far away from truth (when truth is a website that teaches writing skills from a university, as linked).

So I'd vote 1) let it be an "mx1" vector :)

:-D awesome. "an" it is. It just SOUNDS better.

MIKE

Apparently unless the 'm' sounds like an 'em' check this out http://www.dailywritingtips.com/when-to-use-an/

'An' is used before a word starting in a vowel or certain word beginning with "H". For example, it used to be "an hotel", however, "an" before an "h" does seem to be falling out of use.

'A' is used otherwise.

Your example sounds more correct because when you are pronouncing the "m", you are effectively inserting an "e" before it. Technically, "a" is right as "m" is a consonant. However, no-one is going to complain if you say an "m".

Ian (Mackem_Beefy)