thank you Sundar,Andy, Partha for your prompt reply.

      as for the "%*%" is matrix multiplication problem sunder here is a sample of what i want...

x <- rnorm(100,17,24) # X values
y <- rnorm(100,7,11)  # Y values

# since X and Y values are independent to get their
# covariance need to multiply each of them with a Matrix say A

A <- matrix(c(10,25,8,40),nrow=2,ncol=2)

 further  i would like to assign both x and y vectors to one variale

 say z <- c(x,y)

  but if i do this  my matrix multiplication fail

    i.e  w <- A%*%z
 Error in A %*% z : non-conformable arguments ??


    so it tired multiply the  X and Y vector individually

 x<- (A%*%x)
 y<- (A%*%y)

 
 Error in A %*% z : non-conformable arguments ??


  the error persist...sunder...

  or anybody who could direct me..?

regards
Kunal





Sundar Dorai-Raj <sundar.dorai-raj@PDF.COM> wrote:
> 
> 
> Kunal Shetty wrote:
> 
> > Dear R- User
> > 
> >     I created  two random number sets using rnorm function and calcuted their respective means. However now I would like to randomly
> > replace some values with NA. Thus create my own test data.
> >       Any help or suggestions on this ?
> > 
> > 
> 
> Use ?sample:
> n <- 100
> x <- rnorm(n)
> x[sample(n, 4)] <- NA
> sum(is.na(x))
> # [1] 4
> 
> >  Also wanted to confirm when multiplying two random number vectors x am y by matrix..is this how i do it.
> > A is the matrix
> >         
> >        z <- c(x,y)    # x and y the two set of vectors
> >     
> >        w <- A%*%Z   # each element in each vector multipled by the matrix .
> > 
> 
> (Be careful: R is case sensitive (z != Z).)
> 
> I'm not really clear what you want here. "%*%" is matrix multiplication
> and "*" is elementwise multiplication. Also using "c" makes a vector or
> length "n = length(x) + length(y)". This implies that "A" above "p x n"
> (i.e. p rows, n columns) and the result "w" would be "p x 1". Please 
> provide an example of what you expect to see by the multiplication.
> 
> --sundar
> 
> > 
> > regards
> > Kunal
> > 
> > ______________________________________________
> > R-help@stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html


