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An asymptotic expansion relevant to the summation of csc

2022-10-10 18:38 作者:Baobhan_Sith  | 我要投稿

It can be shown that?

%5Csum_%7Bk%3D1%7D%5E%7Bn-1%7D%7B%5Cfrac%7B1%7D%7B%5Csin%20%5Cfrac%7Bk%5Cpi%7D%7Bn%7D%7D%7D%3D%5Cfrac%7B2%7D%7B%5Cpi%7Dn%5Cln%20n%2B%5Cfrac%7B2%7D%7B%5Cpi%7D%5Cleft(%20%5Cln%20%5Cfrac%7B2%7D%7B%5Cpi%7D%2B%5Cgamma%20%5Cright)%20n%2B%5Cfrac%7B1%7D%7B%5Cpi%7D%5Csum_%7Bk%3D1%7D%5E%7B%5Cinfty%7D%7B%5Cfrac%7BB_%7B2k%7D%5Czeta%20%5Cleft(%202k%20%5Cright)%20%5Cleft(%202-2%5E%7B2k%7D%20%5Cright)%7D%7Bk2%5E%7B2k-1%7Dn%5E%7B2k-1%7D%7D%7D%0A

Consider following?complex integral

%5Csum_%7Bk%3D1%7D%5E%7Bn-1%7D%7B%5Cfrac%7B1%7D%7B%5Csin%20%5Cfrac%7Bk%5Cpi%7D%7Bn%7D%7D%7D%3D%5Cfrac%7B1%7D%7B2%5Cpi%20i%7D%5Cint_%7B%5CGamma%7D%7B%5Cfrac%7B1%7D%7B%5Csin%20%5Cfrac%7Bx%7D%7Bn%7D%5Ctanh%20x%7Ddx%7D%0A

Where Gamma? is rectangle: %5Cinfty%20i%5Crightarrow%20-%5Cinfty%20i%5Crightarrow%20n%5Cpi%20-%5Cinfty%20i%5Crightarrow%20n%5Cpi%20%2B%5Cinfty%20i%5Crightarrow%20%5Cinfty%20i,

use small?circular arc?with radius r?to bypass 0?and?n%5Cpi

Decompose above complex integral into three parts

%5Csum_%7Bk%3D1%7D%5E%7Bn-1%7D%7B%5Cfrac%7B1%7D%7B%5Csin%20%5Cfrac%7Bk%5Cpi%7D%7Bn%7D%7D%7D%3D%5Cfrac%7B2%7D%7B%5Cpi%7D%5Cint_r%5E%7B%5Cinfty%7D%7B%5Cfrac%7B1%7D%7B%5Csinh%20%5Cfrac%7Bx%7D%7Bn%7D%5Ctanh%20x%7Ddx%7D%2B%5Cfrac%7B1%7D%7B2%5Cpi%20i%7D%5Cint_%7BC_1%7D%7B%5Cfrac%7B1%7D%7B%5Csinh%20%5Cfrac%7Bx%7D%7Bn%7D%5Ctanh%20x%7Ddx%7D%2B%5Cfrac%7B1%7D%7B2%5Cpi%20i%7D%5Cint_%7BC_2%7D%7B%5Cfrac%7B1%7D%7B%5Csinh%20%5Cfrac%7Bx%7D%7Bn%7D%5Ctanh%20x%7Ddx%7D%0A

Where C1 and C2 are both small?circular?arc

Decompose the first integrand into two parts,?expand the second and the third?Integrands into series of x

%3D%5Cfrac%7B2%7D%7B%5Cpi%7D%5Cleft(%20%5Cint_%7B2r%7D%5E%7B%5Cinfty%7D%7B%5Cfrac%7B1%7D%7B%5Csinh%20%5Cfrac%7Bx%7D%7B2n%7D%7D%5Cfrac%7Be%5E%7B-x%7D%7D%7B1-e%5E%7B-x%7D%7Ddx%7D%2B%5Cint_r%5E%7B%5Cinfty%7D%7B%5Cfrac%7B1%7D%7B%5Csinh%20%5Cfrac%7Bx%7D%7Bn%7D%7Ddx%7D%20%5Cright)%20%2B%5Cfrac%7B1%7D%7B2%5Cpi%20i%7D%5Cint_%7BC_1%7D%7B%5Cfrac%7Bn%7D%7Bx%5E2%7Ddx%7D%2B%5Cfrac%7B1%7D%7B2%5Cpi%20i%7D%5Cint_%7BC_2%7D%7B%5Cfrac%7Bn%7D%7Bx%5E2%7Ddx%7D%2BO%5Cleft(%20r%20%5Cright)%20%0A

expand csch into series of x, and work out other three integrals

%3D%5Cfrac%7B2%7D%7B%5Cpi%7D%5Cleft(%202n%5Cint_%7B2r%7D%5E%7B%5Cinfty%7D%7B%5Cfrac%7B1%7D%7Bx%7D%5Cfrac%7Be%5E%7B-x%7D%7D%7B1-e%5E%7B-x%7D%7Ddx%7D%2B2n%5Csum_%7Bk%3D2%7D%5E%7B%5Cinfty%7D%7B%5Cfrac%7BB_k%5Cleft(%202-2%5Ek%20%5Cright)%7D%7Bk!2%5Ekn%5Ek%7D%7D%5Cint_r%5E%7B%5Cinfty%7D%7B%5Cfrac%7Bx%5E%7Bk-1%7De%5E%7B-x%7D%7D%7B1-e%5E%7B-x%7D%7Ddx%7D-n%5Cln%5Ctanh%20%5Cfrac%7Br%7D%7B2n%7D%20%5Cright)%20-%5Cfrac%7B2n%7D%7B%5Cpi%20r%7D%2BO%5Cleft(%20r%20%5Cright)%20%0A

According to this article: https://zhuanlan.zhihu.com/p/430027389

%3D%5Cfrac%7B2%7D%7B%5Cpi%7D%5Cleft(%20%5Cbegin%7Barray%7D%7Bc%7D%0A%092n%5Cleft(%20%5Cfrac%7B1%7D%7B2r%7D%2B%5Cfrac%7B1%7D%7B2%7D%5Cln%20r%2B%5Cfrac%7B%5Cgamma%7D%7B2%7D-%5Cfrac%7B1%7D%7B2%7D%5Cln%20%5Cpi%20%2BO%5Cleft(%20r%20%5Cright)%20%5Cright)%5C%5C%0A%09%2B%5Csum_%7Bk%3D2%7D%5E%7B%5Cinfty%7D%7B%5Cfrac%7BB_k%5Cleft(%202-2%5Ek%20%5Cright)%7D%7Bk!2%5E%7Bk-1%7Dn%5E%7Bk-1%7D%7D%7D%5Cint_0%5E%7B%5Cinfty%7D%7B%5Cfrac%7Bx%5E%7Bk-1%7De%5E%7B-x%7D%7D%7B1-e%5E%7B-x%7D%7Ddx%7D-n%5Cln%20r%2Bn%5Cln%202%2Bn%5Cln%20n%2BO%5Cleft(%20r%20%5Cright)%5C%5C%0A%5Cend%7Barray%7D%20%5Cright)%20-%5Cfrac%7B2n%7D%7B%5Cpi%20r%7D%2BO%5Cleft(%20r%20%5Cright)%20%0A

Take the limit?as?r?tend to 0.

%5Csum_%7Bk%3D1%7D%5E%7Bn-1%7D%7B%5Cfrac%7B1%7D%7B%5Csin%20%5Cfrac%7Bk%5Cpi%7D%7Bn%7D%7D%7D%3D%5Cfrac%7B2%7D%7B%5Cpi%7Dn%5Cln%20n%2B%5Cfrac%7B2%7D%7B%5Cpi%7D%5Cleft(%20%5Cln%20%5Cfrac%7B2%7D%7B%5Cpi%7D%2B%5Cgamma%20%5Cright)%20n%2B%5Cfrac%7B1%7D%7B%5Cpi%7D%5Csum_%7Bk%3D1%7D%5E%7B%5Cinfty%7D%7B%5Cfrac%7BB_%7B2k%7D%5Czeta%20%5Cleft(%202k%20%5Cright)%20%5Cleft(%202-2%5E%7B2k%7D%20%5Cright)%7D%7Bk2%5E%7B2k-1%7Dn%5E%7B2k-1%7D%7D%7D%0A


An asymptotic expansion relevant to the summation of csc的評(píng)論 (共 條)

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