R help - May 2010 - Random walk

Hi everybody,


I am trying to generate two random walks with an specific correlation, 
for example, two random walks of 200 time steps with a correlation 0.7.

I built the random walks with:

x<-cumsum(rnorm(200, mean=0,sd=1))
y<-cumsum(rnorm(200, mean=0,sd=1))

but I don't know how to fix the correlation between them.

With white noise is easy to fix the correlation using the function 
rmvnorm in the package mvtnorm

I surfed in the web in the searchable mail archives in the R web site 
but no references appears.

If you have some advices to solve this problems I would be very thankful.

Thanks in advance.

Sergio A. Estay
*CASEB *
Departamento de Ecolog?a
Universidad Catolica de Chile

-- 
?La disciplina no tiene ning?n m?rito en circunstancias ideales. ? ? Habor
Mallow

Sums of correlated increments have the same correlation as the original
variables...

 library(mvtnorm)
 X<- matrix(0,nrow=1000,ncol=2)
 for(i in 1:1000){
 Y <- rmvnorm(1000,mean=mu,sigma=S)
 X[i,] <- apply(Y,2,sum)
 }
 cor(Y)
          [,1]      [,2]
[1,] 1.0000000 0.4909281
[2,] 0.4909281 1.0000000

So, unless you meant that you want the _sample_ correlation to be
pre-specified, you are all set.

albyn

On Sun, May 09, 2010 at 09:20:25PM -0400, Sergio Andr?s Estay Cabrera
wrote:
> Hi everybody,
>
>
> I am trying to generate two random walks with an specific correlation, for 
> example, two random walks of 200 time steps with a correlation 0.7.
>
> I built the random walks with:
>
> x<-cumsum(rnorm(200, mean=0,sd=1))
> y<-cumsum(rnorm(200, mean=0,sd=1))
>
> but I don't know how to fix the correlation between them.
>
> With white noise is easy to fix the correlation using the function rmvnorm 
> in the package mvtnorm
>
> I surfed in the web in the searchable mail archives in the R web site but 
> no references appears.
>
> If you have some advices to solve this problems I would be very thankful.
>
> Thanks in advance.
>
> Sergio A. Estay
> *CASEB *
> Departamento de Ecolog?a
> Universidad Catolica de Chile
>
> -- 
> ?La disciplina no tiene ning?n m?rito en circunstancias ideales. ? ? Habor
Mallow
>
> ______________________________________________
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