Is it grammatical to finish a sentence with "also"?

In the following text, I wonder if it's grammatical to finish the sentence with also. it does sound weird to me. The sentence sound incomplete somehow and makes the audience wait for more.

Here this equation must be understood to mean not only that both sides have the same value when they are defined, but also that when either side of the equation is undefined, the other is also.

I know it's the other is also [undefined], but I've never seen a construction like that. If it's grammatical, what is it called?

Solution 1:

It's perfectly grammatical, and can be substituted by other words and phrases too and as well.

I don't use also there myself, as it sounds rather American to me, but I accept it.

In this case it is a bit awkward because of the repetition of also so it might be clearer if you used one of the other possibilities.

Traditionally it is simply an adverb.

Solution 2:

I agree with Colin it is grammatical. As noted in question, the word undefined has been elided at the end. I also agree that too or as well can be substituted in place of also , and imagine those might be used more frequently. However, I don't like any of those forms and would use another. In ascending order of preference:

... the other is also.
... the other is, also.
... the other is as well.
... the other is too.
... the other also is undefined.
... the other also is.
... so is the other.

Solution 3:

Try changing the original:

Here this equation must be understood to mean not only that both sides have the same value when they are defined, but also that when either side of the equation is undefined, the other is also.

to this:

This equation assumes that both sides have the same value when both sides are defined or both undefined when either side is undefined.