u0k2.m

一种新的光纤通信调制技术

function [u0]=u0k2(ek,E_nk,var_nk,alpha,beta,k,M)
range_u0;
s0=(ek(k)-E_nk(k)-sqrt((ek(k)-E_nk(k))^2+4*var_nk(k)))/(2*var_nk(k));
if s0<down
    s0=0.99*down;
end
s=s0+1;
s1=s0;
while(abs(s0-s1)>=10^(-15))%开始循环
s=s1;   
phai1=0;
for I=1:2*M+1
    phai1=phai1+(alpha(I)+beta(I)*(1-beta(I)*s))/(1-beta(I)*s)^2;
end
phai1=phai1-1/s-ek(k);
%以上求一阶导
phai2=0;
for I=1:2*M+1
    phai2=phai2+(2*alpha(I)*beta(I)+(beta(I)^2)*(1-beta(I)*s))/(1-beta(I)*s)^3;
end
phai2=phai2+1/s^2;
%以上求二阶导
s1=s-phai1/phai2;
end
u0=s1;