Question: I am trying to understand meaning of the input value of the argument for model in Arima.sim()

The description was brief on the documentation [here](https://stat.ethz.ch/R-manual/R-devel/library/stats/html/arima.sim.html)

I understand that you can simulate AR or MA by simply doing: 

```
arima.sim(model = list(ar=0.9), n = 200

```

What I dont understand is the following: 

```
arima.sim(model = list(order = c(0,1,0)), n = 100, mean = 1)

```

what do the three numbers in order c(0,1,0) represent? I only know that c(0,0,0) would give you a white noise and c(0,1,0) would give you a random walk. But I dont know why so. I have a feeling that this may have to do with statistical knowledge. 

Appreciate if someone can point me to the right place to read. Thank you!

Answer: 
Order stands for ARIMA model type. i. e `order=c(1,0,1)` will give you a ARMA(1,1) model,
`order=c(1,0,0)` will give you an AR(1) model, `order=c(0,0,1)` will give you an MA(1) and so on. ar, ma, and so on parameters specify the coefficients of the model.
`c(0,1,0)` produces white noise after differencing with lag = 1. So, integrating it back will give you random walk.