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21 Multidimensional Theta FunctionsProperties

§21.3 Symmetry and Quasi-Periodicity

Contents
  1. §21.3(i) Riemann Theta Functions
  2. §21.3(ii) Riemann Theta Functions with Characteristics

§21.3(i) Riemann Theta Functions

21.3.1 \theta\left(-\mathbf{z}\middle|\boldsymbol{{\Omega}}\right)=\theta\left(%
\mathbf{z}\middle|\boldsymbol{{\Omega}}\right),
21.3.2 \theta\left(\mathbf{z}+\mathbf{m}_{1}\middle|\boldsymbol{{\Omega}}\right)=%
\theta\left(\mathbf{z}\middle|\boldsymbol{{\Omega}}\right),

when \mathbf{m}_{1}\in{\mathbb{Z}}^{g}. Thus \theta\left(\mathbf{z}\middle|\boldsymbol{{\Omega}}\right) is periodic, with period 1, in each element of \mathbf{z}. More generally,

with \mathbf{m}_{1}, \mathbf{m}_{2}\in{\mathbb{Z}}^{g}. This is the quasi-periodicity property of the Riemann theta function. It determines the Riemann theta function up to a constant factor. The set of points \mathbf{m}_{1}+\boldsymbol{{\Omega}}\mathbf{m}_{2} form a g-dimensional lattice, the period lattice of the Riemann theta function.

§21.3(ii) Riemann Theta Functions with Characteristics

Again, with \mathbf{m}_{1}, \mathbf{m}_{2}\in{\mathbb{Z}}^{g}

21.3.4 \theta\genfrac{[}{]}{0.0pt}{}{\boldsymbol{{\alpha}}+\mathbf{m}_{1}}{%
\boldsymbol{{\beta}}+\mathbf{m}_{2}}\left(\mathbf{z}\middle|\boldsymbol{{%
\Omega}}\right)=e^{2\pi i\boldsymbol{{\alpha}}\cdot\mathbf{m}_{2}}\theta%
\genfrac{[}{]}{0.0pt}{}{\boldsymbol{{\alpha}}}{\boldsymbol{{\beta}}}\left(%
\mathbf{z}\middle|\boldsymbol{{\Omega}}\right).

Because of this property, the elements of \boldsymbol{{\alpha}} and \boldsymbol{{\beta}} are usually restricted to [0,1), without loss of generality.

For Riemann theta functions with half-period characteristics,

See also §20.2(iii) for the case g=1 and classical theta functions.