# Some questions about Hodge-Deligne polynomials

Can you tell me what the Hodge-Deligne polynomial of a point is, i.e. the polynomial $\sum_{p, q} (-1)^{p+q}h^{p, q}(X) x^py^q$ for some algebraic variety $X$ over the complex numbers? Can you also tell me what the Hodge-Deligne polynomial of $A_{\mathbb{C}}^1$ is, i.e. of the affine line?

-
No, I can not. Thus I am asking. – phil Sep 4 '11 at 22:15
Does $X$ have to be proper or projective or something? I assume $h^{p,q}(X)=\dim_\mathbb{C} H^q(X, \Omega^p)$ which doesn't have to be a finite number... – Matt Sep 6 '11 at 17:38
@Matt: Dear Matt, Presumably the $h^{p,q}$s are defined in terms of the mixed Hodge structure on the cohomology of $X$, which means that they are not the same as the dimension of $H^q(X,\Omega^p)$ when $X$ is not proper. Regards, – Matt E Sep 6 '11 at 18:36

Well $h^{p,q}(\mathbb{C}) = h^{p,q}(pt) = 0$ for $(p,q) \neq (0,0)$ and $h^{0,0}(\mathbb{C}) = h^{0,0}(pt) = 1$ (a generator of $H^0(\mathbb{C},A)$ is any non zero constant function $\mathbb{C} \to A$). So the Hodge polynomials are constant equal to 1.