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Apr 24, 2010 at 18:18 comment added Qfwfq Actually, I was trying genus 2, in which case $H^0(X,K_X^2)=S^2H^0(X,K_X)$, so you can use the (tensor products of pairs of elements of the) base I indicated.
Apr 24, 2010 at 18:14 comment added Qfwfq Haha! ;) No, that was just a misprint! I've edited now.
Apr 24, 2010 at 3:48 comment added Sasha I guess the problem with the computation may be due to the fact that the dual of $H^1(X,T_X)$ is NOT $H^0(X,K_X)$, BUT $H^0(X,2K_X)$!
Apr 23, 2010 at 15:48 comment added Qfwfq I was trying to compute the cocycle in H^1(X,T_X) as explained, e.g., in the book by Claire Voisin. You cover the (total space of the family) with affine open sets $V$ so small that you have an isomorphism between each of them and a cartesian product $V_{red}\times \Delta$, then the epsilon components of the "transition functions" give derivations on the coordinate rings of the double intersections: that's the Cech cocycle. - The problem is that it's not obvious (to me) what this trivializing open affines should be in this simple concrete case.
Apr 23, 2010 at 14:50 history answered Kevin H. Lin CC BY-SA 2.5