adjectives - "Inward-pointing" or "inward pointing"

Which one is correct?

The normal vector we mean is the inward-pointing normal.

The normal vector we mean is the inward pointing normal.

Answer

First let me state that this is mostly a matter of style, and if you are writing for an academic or technical publication, you would do well to get a copy of their style guide and look there for your answer.

That said, hyphens in compound adjectives are used for clarity. They are not always necessary, but are used when a compound may be ambiguous, as in

I'm hosting a small car auction

I'm hosting a small-car auction.

Here the first sentence could mean an auction of small cars or a car auction that is small. The second sentence specifies that it is the former.

When an adverb and adjective combine to make a compound adjective, a hyphen is frequently unnecessary, because more often there is less chance for ambiguity.

He was a well known cellist.

Here there is little chance for confusion, so the hyphen may be dropped.

In your example, "inward pointing" and "inward-pointing" are both correct and easily understood. It becomes a matter of style as to which you prefer.