内维尔Θ函数

内维尔Θ函数（Neville Theta functions）共有四个，定义如下：

${\displaystyle NevilleC(z,m)={\frac {{\sqrt {(}}2)*q(m)^{1/4}*(\sum _{k=0}^{\infty }(q(m)^{(}k*(k+1))*cos((1/2)*(2*k+1)*\pi *z/K(m))))}{{\sqrt {(}}K(m))*m^{1/4}}}}$ ${\displaystyle NevilleThetaC(z,m)={\frac {{\sqrt {(}}2*\pi )*q(m)^{1/4}*(\sum _{k=0}^{\infty }(q(m)^{k*(k+1)}*cos((1/2)*(2*k+1)*\pi *z/K(m))))}{{\sqrt {(}}K(m))*m^{1/4}}}}$ ${\displaystyle NevilleThetaD(z,m)={\frac {{\sqrt {(}}(1/2)*\pi )*(1+2*(\sum _{k=1}^{\infty }(q(m)^{(}k^{2})*cos(k*\pi *z/K(m)))))}{{\sqrt {(}}K(m))}}}$ ${\displaystyle NevilleThetaN(z,m)={\frac {{\sqrt {(}}\pi )*(1+2*(\sum _{k=1}^{\infty }((-1)^{k}*q(m)^{k^{2}}*cos(k*\pi *z/K(m)))))}{{\sqrt {(}}2)*(1-m)^{(}1/4)*{\sqrt {K(m)}}}}}$ ${\displaystyle }$

其中

• ${\displaystyle K(m)=EllipticK({\sqrt {(}}m))}$
• ${\displaystyle K'(m)=EllipticK({\sqrt {(}}1-m))}$
• ${\displaystyle q(m)=e^{\frac {-\pi *K(m)}{K'(m)}}}$

尼维尔Θ函数也可以通过雅可比Θ函数的傅里叶级数来定义，并使得尼维尔Θ函数可以进一步被用于定义相对应的雅可比椭圆函数。

${\displaystyle \theta _{c}(z,m)={\frac {{\sqrt {2\pi }}\,q(m)^{1/4}}{m^{1/4}{\sqrt {K(m)}}}}\,\,\sum _{k=0}^{\infty }(q(m))^{k(k+1)}\cos \left({\frac {(2k+1)\pi z}{2K(m)}}\right)}$

${\displaystyle \theta _{d}(z,m)={\frac {\sqrt {2\pi }}{2{\sqrt {K(m)}}}}\,\,\left(1+2\,\sum _{k=1}^{\infty }(q(m))^{k^{2}}\cos \left({\frac {\pi zk}{K(m)}}\right)\right)}$

${\displaystyle \theta _{n}(z,m)={\frac {\sqrt {2\pi }}{2(1-m)^{1/4}{\sqrt {K(m)}}}}\,\,\left(1+2\sum _{k=1}^{\infty }(-1)^{k}(q(m))^{k^{2}}\cos \left({\frac {\pi zk}{K(m)}}\right)\right)}$

${\displaystyle \theta _{s}(z,m)={\frac {{\sqrt {2\pi }}\,q(m)^{1/4}}{m^{1/4}(1-m)^{1/4}{\sqrt {K(m)}}}}\,\,\sum _{k=0}^{\infty }(-1)^{k}(q(m))^{k(k+1)}\sin \left({\frac {(2k+1)\pi z}{2K(m)}}\right)}$

这种定义涉及到第一类完全椭圆积分。

例子

利用Maple,将z=2.5,m=3 代人上列公式，即得： 与wolfram math结果相当^[1] ：

• ${\displaystyle NevilleThetaC(2.5,.3)=-.65900466676738154967}$
• ${\displaystyle NevilleThetaD(2.5,.3)=0.95182196661267561994}$
• ${\displaystyle NevilleThetaN(2.5,.3)=1.0526693354651613637}$
• ${\displaystyle NevilleThetaS(2.5,.3)=0.82086879524530400536}$