[R] saving multiple panes to PNG

[Charles Evans]

After searching multiple combinations of keywords over the past two  
days and downloading n R graphics tutorials, I have not been able to  
find anything online or in my R books about how to save multiple plot  
panes to PNG.

Specifically, I am using the irf() function in the vars package to  
generate plots of Impulse Response Functions:

 > x.data <- cbind(na.omit(returns(p[,2])),na.omit(returns(n[,2])))
 > colnames(x.data) <- c("p.ret","n.ret")
 > x.jo <- ca.jo(x.data,type="trace",ecdet="none",spec="transitory")
 > x.var <- vec2var(x.jo)
 > x.irf <- irf(x.var,n.ahead=30)
 > plot(x.irf)

This results in a plot containing a pair of IRF graphs in Quartz and  
the following message in the Console:

"Hit <Return> to see next plot:"

When one hits <Return>, the next pair of IRF graphs appears in Quartz.

When I try to save the plots to PNG

 > png(...)
 > plot(...)
 > dev.off()

I am able to save only one of the plots.  How does one tell plot() to  
plot first one of the panes and then the second?

Any help would be greatly appreciated.

Yours,

Charles Evans