The whole sample frame is denoted by a matrix (`nrow * ncol`

) in the
plane, and the sample points with equal intervals are drawn out according to
a random starting point. The points being sampled are marked by red circles.

```
library(animation)
ani.options(nmax = 50)
par(mar = rep(1, 4), lwd = 2)
sample.system()
```

plot of chunk demo-a