hist(mtcars$mpg,freq=FALSE,breaks=12,col="red",xlab="Miles Per Gallon",main="Histogram, rug plot, density curve")
rug(jitter(mtcars$mpg))
lines(density(mtcars$mpg,col="blue",lwd=2))


Warning message:
In density.default(mtcars$mpg, col = "blue", lwd = 2) :
  non-matched further arguments are disregarded

想请问下这段警告信息是什么意思？初学者~