I need to plot an AR(1)
graph for the process
y[k] = 0.75 * y[k-1] + e[k] for y0 = 1.
Assume that e[k]
is uniformly distributed on the interval [-0.5, 0.5]
.
I am trying to use arima.sim
:
library(tseries)
y.0 <- arima.sim(model=list(ar=.75), n=100)
plot(y.0)
It does not seem correct. Also, what parameters do I change if y[0] = 10
?
We want to use R base function arima.sim
for this task, and no extra libraries are required.
By default, arima.sim
generates ARIMA with innovations ~ N(0,1)
. If we want to change this, we need to control the rand.gen
or innov
argument. For example, you want innovations from uniform distributions U[-0.5, 0.5]
, we can do either of the following:
arima.sim(model=list(ar=.75), n=100, rand.gen = runif, min = -0.5, max = 0.5)
arima.sim(model=list(ar=.75), n = 100, innov = runif(100, -0.5, 0.5))
Example
set.seed(0)
y <- arima.sim(model=list(ar=.75), n = 100, innov = runif(100, -0.5, 0.5))
ts.plot(y)
In case we want to have explicit control on y[0]
, we can just shift the above time series such that it starts from y[0]
. Suppose y0
is our desired starting value, we can do
y <- y - y[1] + y0
For example, starting from y0 = 1
:
y <- y - y[1] + 1
ts.plot(y)
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