21 Multidimensional Theta Functions21.2 Definitions

§21.1 Special Notation

(For other notation see Notation for the Special Functions.)

g,h positive integers.
\Integer^{g} \Integer\times\Integer\times\cdots\times\Integer (g times).
\Real^{g} \Real\times\Real\times\cdots\times\Real (g times).
\Integer^{{g\times h}} set of all g\times h matrices with integer elements.
\boldsymbol{{\Omega}} g\times g complex, symmetric matrix with \imagpart{\boldsymbol{{\Omega}}} strictly positive definite, i.e., a Riemann matrix.
\boldsymbol{{\alpha}},\boldsymbol{{\beta}} g-dimensional vectors, with all elements in [0,1), unless stated otherwise.
a_{j} jth element of vector \mathbf{a}.
A_{{jk}} (j,k)th element of matrix \mathbf{A}.
\mathbf{a}\cdot\mathbf{b} scalar product of the vectors \mathbf{a} and \mathbf{b}.
\mathbf{a}\cdot\boldsymbol{{\Omega}}\cdot\mathbf{b} [\boldsymbol{{\Omega}}\mathbf{a}]\cdot\mathbf{b}=[\boldsymbol{{\Omega}}\mathbf{b}]\cdot\mathbf{a}.
\boldsymbol{{0}}_{g} g\times g zero matrix.
\mathbf{I}_{g} g\times g identity matrix.
\mathbf{J}_{{2g}} \begin{bmatrix}\boldsymbol{{0}}_{g}&\mathbf{I}_{g}\\
-\mathbf{I}_{g}&\boldsymbol{{0}}_{g}\end{bmatrix}.
S^{g} set of g-dimensional vectors with elements in S.
|S| number of elements of the set S.
S_{1}S_{2} set of all elements of the form “\mbox{element of $S_{1}$}\times\mbox{element of $S_{2}$}”.
S_{1}/S_{2} set of all elements of S_{1}, modulo elements of S_{2}. Thus two elements of S_{1}/S_{2} are equivalent if they are both in S_{1} and their difference is in S_{2}. (For an example see §20.12(ii).)
a\circ b intersection index of a and b, two cycles lying on a closed surface. a\circ b=0 if a and b do not intersect. Otherwise a\circ b gets an additive contribution from every intersection point. This contribution is 1 if the basis of the tangent vectors of the a and b cycles (§21.7(i)) at the point of intersection is positively oriented; otherwise it is −1.
\oint _{a}\omega line integral of the differential \omega over the cycle a.

Lowercase boldface letters or numbers are g-dimensional real or complex vectors, either row or column depending on the context. Uppercase boldface letters are g\times g real or complex matrices.

The main functions treated in this chapter are the Riemann theta functions \mathop{\theta\/}\nolimits\!\left(\mathbf{z}\middle|\boldsymbol{{\Omega}}\right), and the Riemann theta functions with characteristics \mathop{\theta\!\genfrac{[}{]}{0.0pt}{}{\boldsymbol{{\alpha}}}{\boldsymbol{{\beta}}}\/}\nolimits\!\left(\mathbf{z}\middle|\boldsymbol{{\Omega}}\right).

The function \Theta(\boldsymbol{{\phi}}|\mathbf{B})=\mathop{\theta\/}\nolimits\!\left(\boldsymbol{{\phi}}/(2\pi i)\middle|\mathbf{B}/(2\pi i)\right) is also commonly used; see, for example, Belokolos et al. (1994, §2.5), Dubrovin (1981), and Fay (1973, Chapter 1).