如何在格子splom调用中包含平滑的线条？

Consider the following code:

请考虑以下代码:

library(lattice)
m <- matrix(1:16, nrow=4)
splom(m, panel=function(x, y, ...) {
  panel.xyplot(x, y, ...)
  panel.smooth(x, y, ...) ## this line doesn't seem to work
})
libra