θ^⁡(x1+ⅈ⁢y1,x2+ⅈ⁢y2|[ⅈ-12-12ⅈ])=∑n1=-∞∞∑n2=-∞∞ⅇ-π⁢(n1+y1)2-π⁢(n2+y2)2⁢ⅇπ⁢ⅈ⁢(2⁢n1⁢x1+2⁢n2⁢x2-n1⁢n2).