Hi megh,
Perhaps?

# Data
x = vector("list")
for (i in 1:5) x[[i]] = rnorm(2)

# 2x2 matrices
res <- lapply(x, function(a) a %*% t(a) )
res

# Funcion from ?Reduce
add <- function(x) Reduce("+", x)

# Summing up!
add(res)

See ?lapply and ?Reduce for more information.

HTH,

Jorge


On Wed, Jul 22, 2009 at 3:18 PM, megh <megh700004@yahoo.com> wrote:

>
> Hi,
> I have created a list object like that :
> x = vector("list")
> for (i in 1:5) x[[i]] = rnorm(2)
> x
>
> Now I want to do two things :
> 1. for each i, I want to do following matrix calculation : t(x[[i]]) %*%
> x[[i]] i.e. for each i, I want to get a 2x2 matrix
> 2. Next I want to get  x[[1]] + x[[2]] +....
>
> I did following : res=vector("list"); res = sapply(x, function(i) t(x[[i]])
> %*% x[[i]])
> However above syntax is not giving desired result. Any suggestion please?
>
> --
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