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Jun 23, 2010 at 4:51 vote accept Simon Rose
Jun 23, 2010 at 2:29 comment added Victor Protsak Theta functions depend to two variables, $\tau$ in the Siegel upper half-plane $S_g$ and $z$ in $\mathbb{C}^g.$ Your theta function of the lattice $\vartheta_\Lambda$ (corresponding to $g=1$ is known as a theta-$\textit{constant},$ precisely because the "main" variable $z$ has been set to $0.$ Mumford's book explains it well. Let me just add that the role of the lattice is complementary: it accounts for the Howe duality between an auxiliary orthogonal group $O(\Lambda)$ of isometries of $\Lambda$ and the symplectic group $Sp_{2g}.$
Jun 23, 2010 at 0:18 comment added Wadim Zudilin There is a very nice old (around 1900) book of Krazer on theta functions in several variables (it's in German). Otherwise Mumford's Tata lectures on theta are still very comprehensive. There was a 2-volume proceedings edition of a conference on Theta functions (published by AMS in 1989); it contains some good surveys on the subject.
Jun 22, 2010 at 23:13 answer added SandeepJ timeline score: 7
Jun 22, 2010 at 20:49 answer added S. Carnahan timeline score: 2
Jun 22, 2010 at 20:31 comment added Helge The ones for Z^g have applications to completely integrable systems. See mat.univie.ac.at/~gerald/ftp/book-jac/jacop.pdf . Or the book by Gesztesy, Holden, Michor, and Teschl (not available online, afaik).
Jun 22, 2010 at 19:01 history asked Simon Rose CC BY-SA 2.5