phi_nk_two.m

一种新的光纤通信调制技术

function y = Phi_nk_two(alpha, beta, s) 
%%%%%%    \phi_nk(s) 的二阶导数

a=alpha(:);
b=beta(:);
I=ones(size(a));
[n1 , m1] =size (a) ;
[n2 , m2] =size(b) ;
if (m1~=1) | (m2~=1),
    error('x and nu must be vectors') ;
end ;
if(n1~=n2)
    error('x and nu must be of the same length');
end ;
if(s==0) 
    s = eps;
end

%%%

 y = sum( ( 2*a.*b+(b.^2).*(I-b*s) )./( (I-b*s).^3 ) )  + 1/(s.^2);


if s>0           %%%对此处有疑问， 无论s是否大于0，应该都是 1/s^2 才对；
    ds=-1/s^2;
else
    ds=1/s^2;
end

%%% y = sum( ( 2*a.*b+(b.^2).*(I-b*s) )./( (I-b*s).^3 ) )  - ds;

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