我做了下面的图表
用命令
boxplot(tstats,names=c(expression(bar(x)),"","med(x)","","mad(x)","",
var(x)","",expression(q[.75]-q[.25]),""),
col=rep(c("wheat","chocolate"),5))
abline(h=2,col="steelblue",lty=2)
abline(h=-2,col="steelblue",lty=2)
title(main="normal data")
但我想将两个(小麦和巧克力)盒子之间的共享名称居中。如何修改第一个轴标签?