Load library “astsa” and set working directory

library(astsa)
library(fGarch)
## Loading required package: timeDate
## Loading required package: timeSeries
## Loading required package: fBasics
## 
## Attaching package: 'fBasics'
## The following object is masked from 'package:astsa':
## 
##     nyse
# set your working directory

Exercise 1: Seasonal ARIMA

(a) By visually checking, decide what SARIMA models seem appropriate, i.e., specify p, d, q and P,D,Q in SARIMA model, ARIMA(p, d, q) ∗ ARIMA(P,D, Q)𝑠. Choose the most appropriate two models and explain your answer.

load("Electricity.RData")
plot.ts(electricity)

log.electricity = log(electricity)
plot.ts(log.electricity)

diff.log.electricity = diff(log.electricity, lag = 1)
plot.ts(diff.log.electricity)