"a" RKHS or "an RKHS"

Question

I am confused if I should use "a" or "an" before RKHS (reproducing kernel Hilbert space). Since "R" is not a vowel, I think I should use "a". But I saw both on Wikipedia.

Can you tell me which is correct?

Thanks, Pan

Answer 1

If you read it as an initialism, by saying the names of the letters, it begins with a vowel (sound), and you’d write an RKHS. If you use it as an abbreviation and actually say the words that it abbreviates, you’d write a RKHS, because it’s a reproducing kernel Hilbert space.