[R] Matrix multiplication and random numbers

[jim holtman]

I am not sure what you mean by being the same each time.  If I make
successive calls to the function, I get different results:

> z
         [,1]
[1,]   0.0000
[2,]   0.0000
[3,] 201.6382
[4,]   0.0000
[5,]   0.0000
[6,]   0.0000
[7,]   0.0000
> matmult(InitialPop,1)
        [,1]
[1,]   0.000
[2,]   0.000
[3,] 130.998
[4,]   0.000
[5,]   0.000
[6,]   0.000
[7,]   0.000
> matmult(InitialPop,1)
         [,1]
[1,]   0.0000
[2,]   0.0000
[3,] 219.5943
[4,]   0.0000
[5,]   0.0000
[6,]   0.0000
[7,]   0.0000
> matmult(InitialPop,1)
         [,1]
[1,]   0.0000
[2,]   0.0000
[3,] 200.0077
[4,]   0.0000
[5,]   0.0000
[6,]   0.0000
[7,]   0.0000
> matmult(InitialPop,1)
         [,1]
[1,]   0.0000
[2,]   0.0000
[3,] 256.1736
[4,]   0.0000
[5,]   0.0000
[6,]   0.0000
[7,]   0.0000


On Wed, Sep 9, 2009 at 9:36 AM, RFish<tomworthington at talk21.com> wrote:
>
> Dear All
>
> I new to using R and am struggling with some matrix multiplication.
>
> I have two matrices, one containing random numbers, these are multiplied
> together to get another matrix which is different each time. When I put in
> another for loop to repeat this process a multiple times the matrices are
> all the same. I’m sure there is a way to keep the randomness of the
> different matrices but I think I’m putting the for loop in the wrong place.
> Also when I try and save the matrices using write.table only the first one
> is saved
>
> The code so far is below, any help would be greatly appreciated
>
> Cheers
>
> Tom
>
> InitialPop<-matrix(c(500,0,0,0,0,0,0))
>
> matmult<-function(InitialPop,N){
> mat3<-matrix(c(0,rnorm(1,0.6021,0.0987),0,0,0,0,0,0,0,rnorm(1,0.6021,0.0987),0,0,0,0,1.9,0,0,rnorm(1,0.6021,0.0987),0,0,0,4.8,0,0,0,rnorm(1,0.6021,0.0987),0,0,9.7,0,0,0,0,rnorm(1,0.6021,0.0987),0,18,0,0,0,0,0,rnorm(1,0.6021,0.0987),32.6,0,0,0,0,0,0),nrow=7)
>
> for (i in 1:N){
> PVAmatrix<-matrix(c(0,rnorm(1,0.6021,0.0987),0,0,0,0,0,0,0,rnorm(1,0.6021,0.0987),0,0,0,0,1.9,0,0,rnorm(1,0.6021,0.0987),0,0,0,4.8,0,0,0,rnorm(1,0.6021,0.0987),0,0,9.7,0,0,0,0,rnorm(1,0.6021,0.0987),0,18,0,0,0,0,0,rnorm(1,0.6021,0.0987),32.6,0,0,0,0,0,0),nrow=7)
> mat3<-mat3%*%PVAmatrix
> }
>
> ans<-mat3 %*% InitialPop
>
> return(ans)
>
> }
>
> z<-matmult(InitialPop,1)
> for (i in 1:4) print(z[,1])
> write.table((z),"c:\\Documents and Settings\\...........................)
>
> --
> View this message in context: http://www.nabble.com/Matrix-multiplication-and-random-numbers-tp25365184p25365184.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?