θ⁡(z1,z2|[ⅈ-12-12ⅈ])=∑n1=-∞∞∑n2=-∞∞ⅇ-π⁢(n12+n22)⁢ⅇ-ⅈ⁢π⁢n1⁢n2⁢ⅇ2⁢π⁢ⅈ⁢(n1⁢z1+n2⁢z2).