下面的程序运行后， 得到下图， 我想要增加纵坐标的显示范围，比如 纵坐标 y 在区间（-2，-3）和（2，3）对应的图也
显示出来，怎么办呢  ？  多谢了 各位！
h=function(b){
w=(1+b^2)/(1+(b-1)^2)
2*log(w)
}
x=seq(from=-5,to=5,by=0.01)
y=h(x)
plot(x,y,type='l',ylab= "log-likelihood ratio")
arrows(-0.25,-1.76, -5, -2.235717, length = 0,lty = 2)
arrows(1.25,1.76, 5, 2.135717, length = 0,lty = 2)
arrows(-0.25,-2.1, -0.25, 2.1, length = 0,lty = 3)
arrows(1.25, -2.1, 1.25, 2.1, length = 0,lty = 3)
text(-0.06,-1.97,labels = "a")
text(1.43,-1.96,labels = "b")