因为是奇函数:f(x)=2^x / 2^x+1 ,则f(-x)= -f(x) = - 2^x / 2^x + 1设t=-x,x=-t则f(t) = -2^(-t)/2^(-t)+1 = - 1/(2^t+1) 则在x为(-1,0)时,f(x)=- 1/(2^x+1)
f(x) = SGN(x) * 2^(|x|)/(2^(|x|) +1)