Hopefully someone has a good suggestion
for your question. I'd just like to
point out that the generation of the
random walk is pretty much optimized for
worst performance.
A 'for' loop is not necessary and growing
the objects could be a very significant
drag. See Circles 2 and 3 of 'The R Inferno'.
Hint: 'cumsum' will be useful.
On 02/12/2010 15:58, featherbox wrote:
I've wrote some code to simulate a random walk in 2 dimensions on a lattice.
Basically I want to add something in to make it plot it point by point so
you can see what is going on.
Heres my code for the random walk in 2d
RW2D<-function(N)
{
i<-0
xdir<-0
ydir<-0
xpos<-vector()
xpos[1]<-xdir
ypos<-vector()
ypos[1]<-ydir
for (i in 1:N-1)
{
r<-runif(1)
if(r<=0.25) {xdir<-xdir+1}
if(r>0.25&& r<=0.5) {xdir<-xdir-1}
if(r>0.5&& r<=0.75) {ydir<-ydir +1}
if(r>0.75) {ydir<-ydir-1}
xpos[i+1]<-xdir
ypos[i+1]<-ydir
}
return(cbind(xpos,ypos))
}
rw<-RW2D(10000)
xmin<-min(rw[,1])
xmax<-max(rw[,1])
ymin<-min(rw[,2])
ymax<-max(rw[,2])
plot(rw[,1],rw[,2],type="l",xlab="x",ylab="y",main="Random Walk Simulation
In Two Dimensions",col="green4",xlim=range(xmin:xmax),ylim=range(ymin:ymax))
end<-cbind(rw[10000,1],rw[10000,2])
start<-cbind(0,0)
points(start,pch=4,col="red")
points(end,pch=4,col="red")
--
Patrick Burns
pbu...@pburns.seanet.com
http://www.portfolioprobe.com/blog
http://www.burns-stat.com
(home of 'Some hints for the R beginner'
and 'The R Inferno')
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