# Another notation for the dual space

1. Oct 7, 2007

### quasar987

My professor uses the notation Hom(V,$\mathbb{R}$) for the dual space of V. I usually see V* rather. What does the notation Hom(V,$\mathbb{R}$) stands for exactly? I suppose the domain of Hom is wider than just (vector spaces) x (their field).

The notation suggest it is the set of homomorphisms btw V and R, but this would not accurately describe V* because we want the elements of V* to be linear fct, not just group homomorphisms (we need the f(av)=af(v) part of linear too).

So does the notation comes from a more category theory perspective, where linear maps are considered as "vector space homomorphisms" or something like that?

Just thoughts. I just wanna know what the general meaning for Hom is. Thx

2. Oct 7, 2007

### matt grime

What is the definition of the dual space that you have that is _not_ homs into the underlying field? Hom, in the category of vector spaces _means_ linear map. It is nothing to do with group homomorphisms.

3. Oct 7, 2007

### quasar987

The dual space of V to me is the vector space V* of all linear functions from V to its underlying field.

It's the first time I see the notation Hom being used for anything at all, so I am asking what it means in the most general context. Thank you.

4. Oct 7, 2007

### Hurkyl

Staff Emeritus
Hom(X, Y) is the object of all maps from X to Y.

The precise meaning of 'object' and 'map' depends on the context. In this case, 'object' means 'vector space' and 'map' means 'linear transformation'.

5. Oct 7, 2007

### Hurkyl

Staff Emeritus