?ARMAtoMA
#ar=c(phi1,phi2,...phip)
#ma=c(-ma1,...,-maq) because R uses the plus convention for the MA specification
phi1=.7
theta1=.69
max.lag=50
plot(y=c(1,ARMAtoMA(ar=c(phi1),ma=c(-theta1),lag.max=max.lag)),x=0:max.lag,type='h',main="Impulse Response Function",xlab='k')